Systems and methods for producing hydrogen gas

ABSTRACT

An electrolyzer system comprises one or more electrolyzer cells each comprising a first half cell with a first electrode and a second half cell with a second electrode and a controller to control a current applied through the one or more electrolyzer cells, wherein the controller is configured to dynamically set the current density within a current density range of from about 150 mA/cm 2  to about  3000  mA/cm 2 , and wherein the controller is configured to set the current density to a first value when a first condition is met and to a second value when a second condition is met.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority UNDER 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 63/252,552, filed on Oct. 5, 2021,entitled “LOW COST HYDROGEN GAS PRODUCTION,” the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND

As electricity production migrates to lower carbon dioxide (CO₂)footprint technologies, the ability to convert electricity intolow-carbon or zero-carbon transportation fuels is becoming anincreasingly important challenge in mitigating global CO₂ emissions.Among the options for such fuels, hydrogen gas (H₂) has a uniqueadvantage in that its oxidation product is water. Thus, hydrogen gasrepresents a low-carbon transportation fuel if it can be manufacturedwith a low-carbon footprint.

SUMMARY

The present disclosure describes systems and methods that relate to theproduction of hydrogen gas (H₂) via electrolysis of water. Inparticular, the present disclosure describes systems and methods thatallow for low overall plant capital expenditure and that can provide forreduced operating expenses for the production of H₂ gas by waterelectrolysis, e.g., on a cost per kilowatt or a cost per H₂ productioncapacity basis.

In one aspect, the present disclosure describes an electrolyzer systemcomprising one or more electrolyzer cells each comprising a first halfcell with a first electrode and a second half cell with a secondelectrode and a controller to control a current applied through the oneor more electrolyzer cells, wherein the controller is configured todynamically set the current density within a current density range offrom about 150 mA/cm² to about 3000 mA/cm², and wherein the controlleris configured to set the current density to a first value when a firstcondition is met and to a second value when a second condition is met.

In some examples of the foregoing aspect, the first value is at or belowa first percentage of a maximum capacity current density of theelectrolyzer cell and the second value is at or above a secondpercentage of the maximum capacity current density of the electrolyzercell.

In some examples of the foregoing aspects, the first percentage is 20%or less of the maximum capacity current density.

In some examples of the foregoing aspects, the second percentage is 80%or more of the maximum capacity current density.

In some examples of the foregoing aspects, the first half cell comprisesa pan, one or more ribs inside the pan, and a baffle plate coupled tothe one or more ribs, wherein the baffle plate partitions a volume inthe pan to provide a riser region on a first side of the pan proximateto the first electrode and a down-comer region on a second side of thebaffle plate opposite the first side.

In some examples of the foregoing aspects, wherein the riser regionfacilitates gas formed at the first electrode to rise and avoidformation of gas pockets, and wherein the down-corner region facilitatesdownward flow of an electrolyte solution, wherein the rise of the gasand the downward flow of the electrolyte solution causes circulation inthe pan that facilitates thermal equilibrium and reduced temperaturevariation in the electrolyte.

In some examples of the foregoing aspects, the first half cell comprisesa pan, a manifold positioned inside the pan, and an outlet tube exitingthe manifold for electrolyte to exit the pan, wherein a cross-sectionalarea of the manifold is configured so that an electrolyte flow rate anda gas flow rate through the manifold are low enough to avoid slug flowor plug flow.

In some examples of the foregoing aspects, the first half cell comprisesa pan, one or more ribs positioned vertically inside the pan, and aplurality of welds that weld the first electrode to the one or moreribs, wherein the plurality of welds form a distributed array of weldsacross the electrode that distribute current across the electrode duringoperation of the electrochemical cell.

In some examples of the foregoing aspects, each electrolyzer cellfurther comprises a separator between the first half cell and the secondhalf cell, wherein a number, size, and positions of the plurality ofwelds are such that an impact of power dissipation on a temperature ofthe separator is reduced to reduce damage due to high local temperature.

In another aspect, an electrolyzer system comprises a plurality ofelectrolyzer cells, wherein each electrolyzer cell comprises a firsthalf cell with a first electrode, a second half cell with a secondelectrode, and a separator separating the first half cell from thesecond half cell. The electrolyzer system further includes a powersupply configured to apply a current through each of the plurality ofelectrolyzer cells so that a current density through each of pluralityof electrolyzer cells is within a current density range of from about150 mA/cm² to about 3000 mA/cm², and a controller to dynamically controlthe current density of each of the plurality of electrolyzer cellsbetween a first current density range of 750 mA/cm² or less and a secondcurrent density range of 1 mA/cm² or more.

In some examples of the foregoing aspect, the first half cell comprisesa pan, one or more ribs inside the pan, and a baffle plate coupled tothe one or more ribs, wherein the baffle plate partitions a volume inthe pan to provide a riser region on a first side of the pan proximateto the first electrode and a down-comer region on a second side of thebaffle plate opposite the first side.

In some examples of the foregoing aspects, the first half cell comprisesa pan, a manifold positioned inside the pan, and an outlet tube exitingthe manifold for electrolyte to exit the pan, wherein a cross-sectionalarea of the manifold is configured so that an electrolyte flow rate anda gas flow rate through the manifold are low enough to avoid slug flowor plug flow.

In some examples of the foregoing aspects, the first half cell comprisesa pan, one or more ribs positioned vertically inside the pan, and aplurality of welds that weld the first electrode to the one or moreribs, wherein the plurality of welds form a distributed array of weldsacross the electrode that distribute current across the electrode duringoperation of the electrochemical cell.

In some examples of the foregoing aspects, each electrolyzer cellfurther comprises a separator between the first half cell and the secondhalf cell, wherein a number, size, and positions of the plurality ofwelds are such that an impact of power dissipation on a temperature ofthe separator is reduced to reduce damage due to high local temperature.

In another aspect, a method for carrying out electrolysis comprisesdynamically changing a current density associated with an operation ofan electrolyzer within a range of values of about 0.15 A/cm² and 3.0A/cm², wherein the changing of the current density associated with theoperation of the electrolyzer is in response to a change in demand forelectricity within a region where the electrolyzer is located, andwherein the changing of the current density comprises lowering thecurrent density within the range of values of about 0.15 A/cm² and 3.0A/cm² when the demand for electricity increases within the region wherethe electrolyzer is located and raising the current density within therange of values of about 0.15 A/cm² and 3.0 A/cm² when the demand forelectricity decreases within the region where the electrolyzer islocated.

In some examples of the foregoing aspect, the change in demand occursfor a period of time when the demand is fluctuating.

In some examples of the foregoing aspect, the demand fluctuatingcomprises increases and decreases of demand within the period of time.

In some examples of the foregoing aspect, an average demand over theperiod of time is elevated compared to another period of time.

In some examples of the foregoing aspect, an average demand over theperiod of time is decreased compared to another period of time.

In some examples of the foregoing aspect, the period of time is onewhere demand typically increases or decreases.

In some examples of the foregoing aspect, the period of time is betweenspecific hours within a day.

In some examples of the foregoing aspect, the electrolyzer comprises atleast two separate electrolyzer cells.

In some examples of the foregoing aspect, the electrolyzer has a totalsize of at least about 2.5 m³.

In some examples of the foregoing aspect, when the demand forelectricity increases within the region where the electrolyzer islocated, an operating expenditure of the electrolyzer increases unlessthe current density is decreased.

In another aspect, a method for carrying out electrolysis comprises: (a)reducing a current density associated with an operation of anelectrolyzer to 20% or less of a maximum capacity of the current densityof the electrolyzer when demand for electricity increases in a regionwhere the electrolyzer is located, and (b) increasing the currentdensity associated with an operation of an electrolyzer to 80% or moreof a maximum capacity of the current density of the electrolyzer whendemand for electricity decreases in a region where the electrolyzer islocated.

In some examples of the foregoing aspect, the demand for electricityincreases or the demand for electricity decreases during a period oftime when demand is fluctuating.

In some examples of the foregoing aspect, the demand fluctuatingcomprises increases and decreases of demand within the period of time.

In some examples of the foregoing aspect, an average demand over theperiod of time is elevated compared to another period of time.

In some examples of the foregoing aspect, an average demand over theperiod of time is decreased compared to another period of time.

In some examples of the foregoing aspect, the period of time is onewhere demand typically increases or decreases.

In some examples of the foregoing aspect, the period of time is betweenspecific hours within a day.

In some examples of the foregoing aspect, the electrolyzer comprises atleast two separate cells.

In some examples of the foregoing aspect, the electrolyzer has a totalsize of at least 2.5 m³.

In some examples of the foregoing aspect, when the demand forelectricity increases within the region where the electrolyzer islocated, an operating expenditure of the electrolyzer increases unlessthe current density is decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate generally, by way of example, but not by way oflimitation, various embodiments discussed in the present document.

FIG. 1 is a schematic diagram of an example electrolyzer cell for theelectrolysis of water to produce hydrogen gas.

FIG. 2 is a schematic view of a stack comprising a plurality ofelectrolyzer cells configured for the electrolysis of water to producehydrogen gas.

FIG. 3 is a front view of an example pan assembly that can form an anodehalf cell, a cathode half cell, or both in an electrolyzer cell.

FIG. 4 is a side view of the example pan assembly of FIG. 3 .

FIG. 5 is a close-up perspective view of a top portion of the examplepan assembly of FIGS. 3 and 4 , showing a manifold of the pan assembly.

FIG. 6 is a close-up side view of the manifold of the example panassembly of FIGS. 3 and 4 .

FIG. 7 is a first perspective view that conceptually shows the flow ofelectrolyte into the manifold of the example pan assembly of FIGS. 3 and4 .

FIG. 8 is a second perspective view that conceptually shows the flow ofelectrolyte into the manifold of the example pan assembly of FIGS. 3 and4 .

FIG. 9 is a side view of a second example pan assembly that can form ananode half cell, a cathode half cell, or both, in an electrolyzer cell.

FIG. 10 is a front view of the second example pan assembly of FIG. 9 .

FIG. 11 is a perspective view of the second example pan assembly ofFIGS. 9 and 10 , which shows details of a baffle assembly located withinthe second example pan assembly.

FIG. 12 is a perspective view of the second example pan assembly ofFIGS. 9 and 10 with an electrode coupled to the baffle assembly.

FIG. 13 is a cross-sectional side view of the second example panassembly of FIGS. 9 and 10 and a corresponding cross-sectional side viewof a comparative pan assembly that does not include a baffle assembly.

FIG. 14 is schematic side view showing a simulated flow distribution ofelectrolyte within the second example pan assembly of FIGS. 9 and 10compared to a comparative flow distribution within the comparative panassembly.

FIG. 15 is perspective view of a baffle plate that can form part of thebaffle assembly in the second pan assembly of FIGS. 9 and 10 .

FIG. 16 is a front view of a third example pan assembly that can form ananode half cell, a cathode half cell, or both, in an electrolyzer cell.

FIG. 17 is a cross-sectional side view of the third example pan assemblyof FIG. 16 .

FIG. 18 is a close-up cross-sectional side view of the third example panassembly of FIGS. 16 and 17 .

FIG. 19 is a perspective view of the third example pan assembly of FIGS.16 and 17 , which shows details of one or more ribs within the thirdexample pan assembly.

FIGS. 20A-20C show perspective views of various alternative ribstructures for the third example pan assembly of FIGS. 16 and 17 .

FIG. 21 is a schematic diagram of an example electrolyzer cell with anelectrolyte temperature control system.

FIG. 22 is a graph of example electricity prices over the course of atypical 24 hour period.

FIG. 23 is a graph showing an example the operation of electrolyzercells for the generation of hydrogen gas according to the load gainingand load shedding methods of the present disclosure.

FIG. 24 is a graph showing the cost per kilogram of produced hydrogengas for an example electrolyzer cell and the improvement that can beachieved by generating hydrogen gas according to the load gaining andload shedding methods of the present disclosure.

FIG. 25 is a graph showing an optimal operating current density for anexample electrolyzer cell at various electricity prices.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. The exampleembodiments may be combined, other embodiments may be utilized, orstructural, and logical changes may be made without departing from thescope of the present invention. While the disclosed subject matter willbe described in conjunction with the enumerated claims, it will beunderstood that the exemplified subject matter is not intended to limitthe claims to the disclosed subject matter. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined by the appended claims andtheir equivalents.

References in the specification to “one embodiment”, “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited. For example, aconcentration range of “about 0.1% to about 5%” should be interpreted toinclude not only the explicitly recited concentration of about 0.1 wt. %to about 5 wt. %, but also the individual concentrations (e.g., 1%, 2%,3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, and3.3% to 4.4%) within the indicated range. The statement “about X to Y”has the same meaning as “about X to about Y,” unless indicatedotherwise. Likewise, the statement “about X, Y, or about Z” has the samemeaning as “about X, about Y, or about Z,” unless indicated otherwise.

In this document, the terms “a,” “an,” or “the” are used to include oneor more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.Unless indicated otherwise, the statement “at least one of whenreferring to a listed group is used to mean one or any combination oftwo or more of the members of the group. For example, the statement “atleast one of A, B, and C” can have the same meaning as “A; B; C; A andB; A and C; B and C; or A, B, and C,” or the statement “at least one ofD, E, F, and G” can have the same meaning as “D; E; F; G; D and E; D andF; D and G; E and F; E and G: F and G; D, E, and F; D, E, and G; D, F,and G; E, F, and G; or D, E, F, and G.” A comma can be used as adelimiter or digit group separator to the left or right of a decimalmark; for example, “0.000.1”” is equivalent to “0.0001.”

In the methods described herein, the steps can be carried out in anyorder without departing from the principles of the invention, exceptwhen a temporal or operational sequence is explicitly recited.Furthermore, specified steps can be carried out concurrently unlessexplicit language recites that they be carried out separately. Forexample, a recited act of doing X and a recited act of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the process. Recitation ina claim to the effect that first a step is performed, and then severalother steps are subsequently performed, shall be taken to mean that thefirst step is performed before any of the other steps, but the othersteps can be performed in any suitable sequence, unless a sequence isfurther recited within the other steps. For example, claim elements thatrecite “Step A, Step B, Step C, Step D, and Step E” shall be construedto mean step A is carried out first, step E is carried out last, andsteps B, C, and D can be carried out in any sequence between steps A andE (including with one or more steps being performed concurrent with stepA or Step E), and that the sequence still falls within the literal scopeof the claimed process. A given step or sub-set of steps can also berepeated.

Furthermore, specified steps can be carried out concurrently unlessexplicit claim language recites that they be carried out separately. Forexample, a claimed step of doing X and a claimed step of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the claimed process.

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, within 1%, within0.5%, within 0.1%, within 0.05%, within 0.01%, within 0.005%, or within0.001% of a stated value or of a stated limit of a range, and includesthe exact stated value or range.

The term “substantially” as used herein refers to a majority of, ormostly, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%,98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or100%.

In addition, it is to be understood that the phraseology or terminologyemployed herein, and not otherwise defined, is for the purpose ofdescription only and not of limitation. Furthermore, all publications,patents, and patent documents referred to in this document areincorporated by reference herein in their entirety, as thoughindividually incorporated by reference. In the event of inconsistentusages between this document and those documents so incorporated byreference, the usage in the incorporated reference should be consideredsupplementary to that of this document; for irreconcilableinconsistencies, the usage in this document controls.

Hydrogen gas (H₂) can be formed electrochemically by a water-splittingreaction where water is split into oxygen gas (O₂) and H₂ gas at ananode and a cathode of an electrochemical cell, respectively. Examplesof such electrochemical processes include, without limitation, protonelectrolyte membrane (PEM) electrolysis and alkaline water electrolysis(AWE). In such electrochemical reactions, the operating energy necessaryto drive the water-splitting electrolysis reaction is high due toadditional energy costs as a result of various energy inefficiencies.For example, to reduce unwanted migration of ionic species between theelectrodes, the cathode and the anode may be separated by a separator,such as a membrane, which can reduce migration of the ionic species.Although the separator can improve the overall efficiency of the cell,it can come at a cost of additional resistive losses in the cell, whichin turn increases the operating voltage. Other inefficiencies in waterelectrolysis can include solution resistance losses, electric conductioninefficiencies, and/or electrode over-potentials, among others. Thesevarious inefficiencies and the capital costs associated with minimizingthem can play a role in the economic viability of H₂ generation viawater splitting electrolysis.

The methods and systems provided herein relate to unique electrochemicalprocesses that result in efficient, low cost, and low energy productionof H₂ gas.

Electrolyzer Cell

FIG. 1 is a schematic diagram of a generic water electrolyzer cell 100that converts water into hydrogen and oxygen with electrical power isillustrated in FIG. 1 . In an example, the electrolyzer cell 100comprises two half cells: a first half cell 111 and a second half cell121. In an example, the first and second half cells 111, 121 areseparated by a separator 131, such as a membrane 131. In an example, theseparator 131 comprises a porous or an ion-exchange membrane 131. Inexamples wherein the separator 131 comprises an ion-exchange membrane,the ion-exchange membrane can be of different types, such as an anionexchange membrane (AEM), a cation exchange membrane (CEM), a protonexchange membrane (PEM), a bipolar ion exchange membrane (BEM), an ionsolvating membrane (ISM), or a microporous or nanoporous membrane.

In examples where the separator 131 is a cation exchange membrane, thecation exchange membrane can be a conventional membrane such as thoseavailable from, for example, Asahi Kasei Corp. of Tokyo, Japan, or fromMembrane International Inc. of Glen Rock, NJ, USA, or from The ChemoursCompany of Wilmington, DE, USA. Examples of cation exchange membranesinclude, but are not limited to, the membrane sold under the N2030WXtrade name by The Chemours Company and the membrane sold under theF8020/F8080 or F6801 trade names by the Asahi Kasei Corp. Examples ofmaterials that can be used to form a cationic exchange membrane include,but are not limited to, cationic membranes comprising a perfluorinatedpolymer containing anionic groups, for example sulphonic and/orcarboxylic groups. It may be appreciated, however, that in someexamples, depending on the need to restrict or allow migration of aspecific cation or an anion species between the electrolytes, a cationexchange membrane that is more restrictive and thus allows migration ofone species of cations while restricting the migration of anotherspecies of cations may be used. Similarly, in some embodiments,depending on the need to restrict or allow migration of a specific anionspecies between the electrolytes, an anion exchange membrane that ismore restrictive and thus allows migration of one species of anionswhile restricting the migration of another species of anions may beused. Such restrictive cation exchange membranes and anion exchangemembranes are commercially available and can be selected by oneordinarily skilled in the art.

In some examples, the separator 131 can be selected so that it canfunction in an acidic and/or an alkaline electrolytic solution, asappropriate. Other properties for the separator 131 that may bedesirable include, but are not limited to, high ion selectivity, lowionic resistance, high burst strength, and high stability inelectrolytic solution in a temperature range of room temperature to 150°C. or higher.

In an example, the separator 131 is stable in a temperature range offrom about 0° C. to about 150° C., for example from about 0° C. to about100° C., such as from about 0° C. to about 90° C., for example fromabout 0° C. to about 80° C., such as from about 0° C. to about 70° C.,for example from about 0° C. to about 60° C., such as from about 0° C.,to about 50° C., for example from about 0° C. to about 40° C., or suchas from about 0° C. to about 30° C.

It may be useful to use an ion-specific ion exchange membrane thatallows migration of one type of ion (e.g., cation for a CEM and anionfor an AEM) but not another, or migration of one type of ion and notanother, to achieve a desired product or products in the electrolytesolution.

In an example, the first half cell 111 comprises a first electrode 112,which can be placed proximate to the separator 131, and the second halfcell 121 comprises a second electrode 122, which can be placed proximateto the separator 131, for example on an opposite side of the separator131 from the first electrode 112. In an example, the first electrode 112is the anode for the electrolyzer cell 100 and the second electrode 122is the cathode for the electrolyzer cell 100, such that for theremainder of the present disclosure the first half cell 111 may also bereferred to as the anode half cell 111, the first electrode 112 may alsobe referred to as the anode 112, the second half cell 121 may also bereferred to as the cathode half cell 121, and the second electrode 122may also be referred to as the cathode 122. Each of the electrodes 112,122 can be coated with one or more electrocatalysts to speed thereaction toward the hydrogen gas (H₂ gas) and/or the oxygen gas (O₂gas). Examples of electrocatalysts include, but are not limited to,highly dispersed metals or alloys of platinum group metals, such asplatinum, palladium, ruthenium, rhodium, iridium, or their combinationssuch as platinum-rhodium, platinum-ruthenium, a nickel mesh coated withruthenium oxide (RuO₂), or a high-surface area nickel.

The ohmic resistance of the separator 131 can affect the voltage dropacross the anode 112 and the cathode 122. For example, as the ohmicresistance of the separator 131 increases, the voltage across the anode112 and the cathode 122 may increase, and vice versa. In an example, theseparator 131 has a relatively low ohmic resistance and a relativelyhigh ionic mobility. In an example, the separator 131 has a relativelyhigh hydration characteristics that increase with temperature, and thusdecreases the ohmic resistance. By selecting a separator 131 with lowerohmic resistance known in the art, the voltage drop across the anode 112and the cathode 122 at a specified temperature can be lowered.

In an example, the anode 112 is electrically connected to an externalpositive conductor 116 and the cathode 122 is electrically connected toan external negative conductor 126. When the separator 131 is wet and isin electrolytic contact with the electrodes 112 and 122, and anappropriate voltage is applied across the conductors 116 and 126, O₂ gasis liberated at the anode 112 and H₂ gas is liberated at the cathode122. In certain configurations, an electrolyte, e.g., one comprising ofa solution of KOH in water, is fed into the half cells 111, 121. Forexample, the electrolyte can flow into the anode half cell 111 through afirst electrolyte inlet 114 and into the cathode half cell 121 through asecond electrolyte inlet 124. In an example, the flow of the electrolytethrough the anode half cell 111 picks up the produced O₂ gas as bubbles113, which exits the anode half cell 111 through a first outlet 115.Similarly, the flow of the electrolyte through the cathode half-cell 121can pick up the produced H₂ gas as bubbles 123, which can exit thecathode half cell 121 through a second outlet 125. The gases can beseparated from the electrolyte downstream of the electrolyzer cell 100with one or more appropriate separators. In an example, the produced H₂gas is dried and harvested into high pressure canisters or fed intofurther process elements. The O₂ gas can be allowed to simply vent intothe atmosphere or can be stored for other uses. In an example, theelectrolyte is recycled back into the half cells 111, 121 as needed.

In an example, a controller 128 can be included to control the currentapplied through the electrolyzer cell 100 (for example by controlling avoltage that is applied across the conductors 116 and 126). In anexample, the controller 128 can be configured to control an operatingcurrent density for the cell 100 (e.g., by applying a current thatcorresponds to a desired current density based on the area of the cell100) so that the current density for the cell 100 can be controlled(e.g., for load gaining or load shedding as described in more detailbelow).

In an example, a typical voltage across the electrolyzer cell 100 isfrom about 1.5 volts (V) to about 3.0 V. In an example, an operatingcurrent density for the electrolyzer cell 100 is from about 0.1 A/cm² toabout 3 A/cm². Each cell 100 has a size that is sufficiently large toproduce a sizeable amount of H₂ gas when operating at these currentdensities. In an example, a cross-sectional area of each cell 100 (e.g.,a width multiplied by a height for a rectangular cell) is from about0.25 square meters (m²) to about 15 m², such as from about 1 m² to about5 m², for example from about 2 m² to about 4 m², such as from about 2.25m² to about 3 m², such as from about 2.5 m² to about 2.9 m². In anexample, the total volume of each cell (e.g., a width multiplied by aheight multiplied by a depth) is from about 0.1 cubic meter (m³) toabout 2 m³, such as from about 0.15 m³ to about 1.5 m³, for example fromabout 0.2 m³ to about 1 m³, such as from about 0.25 m³ to about 0.5 m³,for example from about 0.275 m³ to about 0.3 m³. In an example, thetotal volume of the entire electrolyzer system (e.g., the combinedvolume of all the cells in all the stacks in the plant) is from about 1m³ to about 200 m³, such as from about 2 m³ to about 100 m³, for examplefrom about 2.5 m³ to about 50 m³.

As will be appreciated by those having skill in the art, operating anelectrical power bus at such a low voltage and high current density canbe highly inefficient. Therefore, typically a plurality of theelectrolyzer cells 100 are assembled and electrically connected inseries into an electrolyzer stack. Each of the plurality of cells 100can operate at a lower higher voltage and at the same current density asa single electrolyzer cell 100, which makes the system far moreefficient. In an example, an electrolyzer stack can comprise from aboutfive (5) electrolyzer cells 100 to about 500 electrolyzer cells 100, forexample eighty (80) electrolyzer cells 100 or more connected in seriesto provide an electrolyzer stack.

Electrolyzer Stack

FIG. 2 shows a schematic diagram of a portion of such an electrolyzerstack 130 of electrolyzer cells 132A-132N (collectively referred to as“electrolyzer cells 132” or “electrolyzer cell 132”). Each cell 132 inthe stack 130 can have any one of the structures described above withrespect to the example electrolyzer cell 100 of FIG. 1 , e.g., with oneor both of the anode half cell 111 and the cathode half cell 121. Inaddition, each cell 132 can include one or more structures of the cellassemblies (e.g., comprising one or more structures of the panassemblies described below). As will be appreciated by those havingskill in the art, the structures of the cell assemblies (i.e., forindividual pan assemblies) can provide for the overall lower cost H₂production described herein.

In an example, the electrolyzer cells 132 are connected electrically inseries with conductors 304. In an example, the stack 130 comprises alarge number of electrolyzer cells 132 connected in series, e.g., fifty(50) or more electrolyzer cells 132, sixty (60) or more electrolyzercells 132, seventy (70) or more electrolyzer cells 132, eighty (80) ormore electrolyzer cells 132, ninety (90) or more electrolyzer cells 132,one hundred (100) or more electrolyzer cells 132, one hundred fifty(150) or more electrolyzer cells 132, two hundred (200) or moreelectrolyzer cells 132, three hundred (300) or more electrolyzer cells132, and so on. The individual electrolyzer cells 132 in the exampleelectrolyzer stack 130 are labeled with reference numbers 132A through132N, with only the first electrolyzer cell 132A, the secondelectrolyzer cell 132B, and the last electrolyzer cell 132N being shownin FIG. 2 . In an example, the electrical positive conductor (e.g., thepositive conductor 116 in FIG. 1 ) of one cell 132A is electricallyconnected to the electrical negative conductor of the subsequent cell132B (e.g., the negative conductor 126 in FIG. 1 ) with a connectingconductor 134, with the following exceptions: (a) the positive conductorof the final cell 132N at the highest voltage is connected to a powersupply 136; and (b) the negative conductor of the first cell 132A at thelowest voltage is connected to a ground 138 of the electrical circuit.In an example, the power supply 136 is a constant-currentvoltage-limited rectifier that converts grid AC power to a suitable DCpower level. In an example, the power supply 136 can be controlled by acontroller that is configured to control the current density of theelectrolyzer cells 132 in the stack 130 (similar to the controller 128described above with respect to FIG. 1 ), for example to allow the stackto be dynamically operated for load gaining or load shedding in responseto fluctuations in electricity demand and/or price (as described in moredetail below).

Electrolyzer Cell Pan Assembly

The physical configuration of the electrolyzer cell 100 can be anyphysical structure configured to allow for the liberation of oxygen gasat the anode 112 and for the liberation of hydrogen gas at the cathode122. In an example, the electrolyzer cell 100 can comprise componentsthat can dynamically operate at high current densities (e.g., at 2 A/cm²or higher). By providing for operation at high current densities, theelectrolyzer cells 100 can allow operators to meet their targetedproduction rate with fewer cells, thereby reducing capital expenses. Inaddition, by allowing the electrolyzer cells 100 to dynamically operateover a wide range of operational current densities, the electrolyzercells 100 can provide operators with a large turndown ratio, which canenable the operators to maximize production when power prices are low,and to reduce power consumption when power prices are high (as describedin more detail below).

The operation of electrolyzer cells at high current densities can resultin significant challenges, such as, but not limited to, large gasvolumes produced at high current densities, significant temperature andpressure fluctuations, membrane erosion or fatigue, large amount of heatgenerated in the cell, and/or high flow rates of electrolyte. Therefore,in an example, each electrolyzer cell 100 can include a configuration ofan anode pan assembly and/or a cathode pan assembly that can overcomeone or more of these challenges, such as, but not limited to, reducingor minimizing large temperature variations of the electrolyte along theheight of the cell; reducing or minimizing masking of the nominal activearea with gas; reducing or minimizing formation of a stagnant gas pocketthat can result in localized drying out of the membrane; and/or reducingor minimizing significant pressure fluctuations due to slug or plug flowat the cell outlets.

Due to large gas volumes, static gas pockets can form on the electrodeor at the top of the cell. Providing high electrolyte flow rates andutilizing features that cause gas lift to create high local shear ratesmay help to minimize static gas pocket formation on the electrode.However, a high electrolyte flow rate coupled with large production ofgas and large amounts of electrolyte solution entering and exiting thecell presents significant challenges associated with slug and plug flow.This type of flow can be reduced or minimized by using a specifiedmanifold and the outlet tube configuration, described in more detailbelow.

In some examples, a pan assembly can be used on the anode or the cathodeside of the electrolyzer cell 100. The pan assembly can include aneffective collection system at the top of the cell to minimize and insome cases prevent the formation of large stagnant gas pockets at thetop of the cell. In an example, the collection system comprises amanifold and an outlet tube with large cross-sectional area thateffectively provides space for gas to collect as well as electrolyte toflow while also reducing or minimizing the likelihood of masking of themembrane and/or slug or plug flow. The pan assembly can provide for twophase (gas/liquid) flow that is effectively directed out of the cell.

The pan assembly, manifold, and outlet tube are designed to ensure thatflow is uniform or substantially across the width of the cell, and thatpressure fluctuations within the cell is minimal. The flow uniformitydrives the need to ensure that the back pressure associated with theflow's entry into the manifold is significantly greater than thepressure drop along the length of the manifold and so that the pressurewithin the manifold is greater than the pressure drop exiting themanifold. Maintaining an essentially constant internal pressuredistribution drives the requirement to avoid slug or plug flow throughthe manifold and the outlet tubing. Therefore, the pan assemblycomprising the manifold and the outlet tube can provide for reliablecell operation across a high range of electrolyte flows and high currentdensities.

As the current density is increased in the cell, power dissipation canalso rise dramatically. Large spatial and/or temporal temperaturefluctuations can damage the membrane. The contribution of internal powerdissipation to the cell's internal temperature distribution can bereduced or minimized through operating conditions such as themaintaining temperature, flow rate of the inflowing electrolyte, and/orre-circulation of the inflowing electrolyte. High electrolyte flow ratescan provide for a high amount of convective heat transfer within thecell, thereby helping to reduce or minimize the heat buildup andconcomitant temperature rise within the cell that may otherwise resultfrom an increase in current density. In an example, the pan assembly ofthe electrolyzer cell includes a baffle plate configuration inside thepan assembly that can reduce or minimize the impact of fluctuating powerdissipation on the internal temperature of the cell by helping to ensurethat the electrolyte remains isothermal or substantially isothermalalong the height of the cell and so that thermal equilibrium is achievedrapidly after the operating current density is changed.

In the generic electrolyzer cell 100 described above with respect toFIG. 1 , the anode half cell 111 can comprise an anode pan assembly thatincludes the anode 112 and the anode electrolyte (also referred to as“anolyte”). Similarly, the cathode half cell 121 can comprise a cathodepan assembly that includes the cathode 122 and the cathode electrolyte(also referred to as “catholyte”). The anode pan assembly and thecathode pan assembly can be separated by the separator 131 (e.g., adiaphragm, a membrane electrode assembly (MEA), one or more ion exchangemembranes (IEM), or another type of membrane or separator). The anodepan assembly and/or the cathode pan assembly can include components,such as a collection system that collects the gas and the electrolytefor flow out of the cell 100. A separator assembly can include one ormore of an anion exchange membrane (AEM), a cation exchange membrane(CEM), or another separator depending on the desired reactions at theanode 112 and the cathode 122. In between these components, variousadditional separator components can be provided, e.g., to separate themembrane 131 from the anode 112, to separate the membrane 131 from thecathode 122, as well as provide mechanical integrity to the membranes orother separator structures. In addition to these components, individualgaskets or gasket tape may be provided in between and along the outerperimeter of the components to seal the compartments from fluid leakage.

In an example, all of the components described above are alignedparallel or substantially parallel to each other and optional peripheralbolting may be provided to stack them together in the electrochemicalcell 100. In a filter press configuration, no peripheral bolting may berequired. In a stack of electrochemical cells, the anode 112 of oneelectrochemical cell 100 can be electrically connected with the cathode122 of an adjacent electrochemical cell. The current passes through thestack of electrochemical cells during operation.

FIGS. 3-8 show several views of an example pan assembly 140 that can beused as the anode pan assembly for the anode half cell 111 or as thecathode pan assembly for the cathode half cell 121 in the electrolyzercell 100 shown in FIG. 1 or in one of the individual electrolyzer cells132 in the stack 130 of FIG. 2 . FIG. 3 is a front view of the panassembly 140 and FIG. 4 is a cross sectional view of the pan assembly140. It is to be understood that in the electrochemical cell 100 or 132,the pan assembly 140 can be used as the anode pan assembly or as thecathode pan assembly, or both, depending on the need and the reaction atthe anode 112 and the cathode 122. The next component of the cell suchas the anode 112 or the cathode 122 can be placed on top of the panassembly 140 shown the front view of FIG. 3 .

As illustrated in FIGS. 3 and 4 , the pan assembly 140 includes a pan142. Inside the depth of the pan 142 and at the top of the pan 142 ishoused a manifold 144 (shown in FIG. 4 ). The manifold 144 can beconnected to one or more outlet tubes 146 depending on the requirementsfor the electrolyzer cell 100. For example, the design can incorporate2, 3, 4, or more outlet tubes 146 on each pan assembly 140, on the sameor either side of the pan 142 in order to minimize the cell thickness,and maximize the number of cells 100 that can fit in an electrolyzerframe of a particular size. FIGS. 5 and 6 show close-up details of themanifold 144 and the outlet tube 146.

In an example, a depth D_(Manifold) of the manifold 144 and/or the crosssectional area of the manifold 144 and/or a size of the outlet tube 146is selected so that the pan assembly 140 provides a relatively largecross sectional area of the manifold 144 in order to reduce or minimizethe occurrence of slug and plug flow of the two phase system, but alsoto provide enough space between a wall of the manifold 144 and theelectrode placed on top of the pan 142 (e.g., the anode or the cathodedepending on whether the pan assembly 140 forms an anode pan or acathode pan) for the gas and electrolyte to have an unimpeded flow andfor the membrane to stay wetted. The depth DManifold of the manifold 144and/or the cross sectional area of the manifold 144 and/or a size of theoutlet tube 146 can also dictate the overall thickness of the cell 100.

In an example of the pan assembly 140, the manifold 144 has a depthD_(Manifold) (shown in FIGS. 5 and 6 ) that is from about 0.25 (25%) toabout 0.75 (75%) of a depth D_(Pam) of the pan 142, for example fromabout 0.25 (25%) to about 0.6 (60%) of the depth D_(Pan), such as fromabout 0.25 (25%) to about 0.5 (50%) of the depth D_(pan) of the pan 142,for example from about 0.25 (25%) to about 0.4 (40%) of the depthD_(Pan) of the pan 142, such as from about 0.25 (25%) to about 0.3 (30%)of the depth D_(Pan) of the pan 142, for example from about 0.3 (30%) toabout 0.75 (75%) of the depth D_(Pan) of the pan 142, such as from about0.3 (30%) to about 0.6 (60%) of the depth D_(Pan) of the pan 142, forexample from about 0.3 (30%) to about 0.5 (50%) of the depth D_(Pan) ofthe pan 142, such as from about 0.3 (30%) to about 0.4 (40%) of thedepth D_(Pan) of the pan 142, for example from about 0.4 (40%) to about0.75 (75%) of the depth D_(Pan) of the pan 142, such as from about 0.4(40%) to about 0.6 (60%) of the depth D_(Pan) of the pan 142, forexample from about 0.4 (40%) to about 0.5 (50%) of the depth D_(Pan) ofthe pan 142, such as from about 0.5 (50%) to about 0.75 (75%) of thedepth D_(Pan) of the pan 142, for example from about 0.5 (50%) to about0.6 (60%) of the depth D_(Pan) of the pan 142, such as from about 0.6(60%) to about 0.75 (75%) of the depth D_(Pan) of the pan 142.

In an example, the manifold 144 has an upward taper at the top (bestseen in FIG. 6 ). The upward taper creates an internal volume or zoneabove the upper edge of the membrane 131 positioned next to theelectrode, providing a small region for a gas-rich mixture to formwithout resulting in the drying out of the membrane 131.

An example flow path for the gas and electrolyte mixture through the panassembly 140 is shown by the dotted line 148 in FIGS. 7 and 8 . As canbe seen in FIGS. 7 and 8 , in an example, the flow path 148 of the twophases of the gas and the electrolyte passes upwards from the main partof the pan 142 to the top of the manifold 144 and then down into themanifold 144 through a set of notches 150 at the top of the manifold144. The gas and the electrolyte can then flow out through the outlettube 146.

In order to accommodate a large amount of the gas and the electrolytesolution flowing though the manifold 144 and the outlet tube 146, e.g.,due to high current densities and high flow rates, and to reduce orminimize the occurrence of slug and plug flow, in an example, the crosssectional area of the manifold 144 and the outlet tube 146 is largeenough to maintain the superficial liquid velocity of the electrolyte tobe about 0.35 m/s or less, for example about 0.25 m/s or less, such asabout 0.2 m/s or less, for example about 0.15 m/s or less, such as about0.1 m/s or less, for example about 0.08 m/s or less, such as about 0.05m/s or less, for example about 0.01 m/s or less. The cross sectionalarea of the manifold 144 and the outlet tube 146 is large enough tomaintain a superficial gas velocity (e.g., O₂ gas from an anode pan orH₂ gas produced from the cathode pan) to be about 5 m/s or less, forexample about 4.5 m/s or less, such as about 4 m/s or less, for exampleabout 3.5 m/s or less, such as about 3 m/s or less, for example about2.5 m/s or less, such as about 2 m/s or less, for example about 1.5 m/sor less, such as about 1 m/s or less.

In order to accommodate the high current densities and the high flowrates as noted herein, in some examples, the cross sectional area of themanifold 144 (e.g. comprising the depth D_(Manifold) of the manifold 144of from about 0.25 (25%) to about 0.75 (75%) of the depth D_(Pan) of thepan 142) is from about 520 square millimeters (mm²) to about 6200 mm²,for example from about 520 mm² to about 6000 mm², such as from about 520mm² to about 5000 mm², for example from about 520 mm² to about 4000 mm²,such as from about 520 mm² to about 3000 mm², for example from about 520mm² to about 2000 mm², such as from about 520 mm² to about 1000 mm², forexample from about 600 mm² to about 6200 mm², such as from about 600 mm²to about 6000 mm², for example from about 600 mm² to about 5000 mm²,such as from about 600 mm² to about 4000 mm², for example from about 600mm² to about 3000 mm², such as from about 600 mm² to about 2000 mm², forexample from about 600 mm² to about 1000 mm², such as from about 800 mm²to about 6200 mm², for example from about 800 mm² to about 6000 mm²,such as from about 800 mm² to about 5000 mm², for example from about 800mm² to about 4000 mm², such as from about 800 mm² to about 3000 mm², forexample from about 800 mm² to about 2000 mm², such as from about 800 mm²to about 1000 mm², for example from about 1000 mm² to about 6200 mm²,such as from about 1000 mm² to about 6000 mm², for example from about1000 mm² to about 5000 mm², such as from about 1000 mm² to about 4000mm², for example from about 1000 mm² to about 3000 mm², such as fromabout 1000 mm² to about 2000 mm², for example from about 2000 mm² toabout 6200 mm², such as from about 2000 mm² to about 6000 mm², forexample from about 2000 mm² to about 5000 mm², such as from about 2000mm² to about 4000 mm², for example from about 2000 mm² to about 3000mm², such as from about 3000 mm² to about 6200 mm², for example fromabout 3000 mm² to about 6000 mm², such as from about 3000 mm² to about5000 mm², for example from about 3000 mm² to about 4000 mm², such asfrom about 4000 mm² to about 62000 mm², for example from about 4000 mm²to about 6000 mm², such as from about 4000 mm² to about 5000 mm², forexample from about 5000 mm² to about 6200 mm², such as from about 5000mm² to about 6000 mm².

In some examples wherein the cross-sectional area of the manifold 144 isas recited above, the outlet tube 146 fluidly connected to the manifold144 can have an equivalent diameter EDoutiet (shown in FIG. 5 ) is fromabout 26 millimeters (mm) to about 89 mm, for example from about 26 mmto about 80 mm, such as from about 26 mm to about 75 mm, for examplefrom about 26 mm to about 70 mm, such as from about 26 mm to about 60mm, for example from about 26 mm to about 50 mm, such as from about 26mm to about 40 mm, for example from about 26 mm to about 30 mm, such asfrom about 30 mm to about 89 mm, for example from about 30 mm to about80 mm, such as from about 30 mm to about 75 mm, for example from about30 mm to about 70 mm, such as from about 30 mm to about 60 mm, forexample from about 30 mm to about 50 mm, such as from about 30 mm toabout 40 mm, for example from about 40 mm to about 89 mm, such as fromabout 40 mm to about 80 mm, for example from about 40 mm to about 75 mm,such as from about 40 mm to about 70 mm, for example from about 40 mm toabout 60 mm, such as from about 40 mm to about 50 mm, for example fromabout 50 mm to about 89 mm, such as from about 50 mm to about 80 mm, forexample from about 50 mm to about 75 mm, such as from about 50 mm toabout 70 mm, for example from about 50 mm to about 60 mm, such as fromabout 60 mm to about 89 mm, for example from about 60 mm to about 80 mm,such as from about 60 mm to about 75 mm, for example from about 70 mm toabout 89 mm, such as from about 70 mm to about 80 mm, for example fromabout 70 mm to about 75 mm.

Those having skill in the art will appreciate that what may beconsidered a “high electrolyte flow rate” may be in comparison to thesize of the electrochemical cell 100. For example, a “high flow rate”for a relatively narrow cell, e.g., from about 300 mm to about 600 mmwide, may correspond to a flow rate of about 200 kg/h, while a “highflow rate” for a large commercial size cell, e.g., from about 2 meters(m) to about 3 m wide, may correspond to a flow rate of about 800 kg/hor more, for example about 1000 kg/h or more, such as about 1350 kg/h ormore, for example about 1500 kg/h or more, such as about 1750 kg/h ormore, for example about 2000 kg/h or more, such as about 2250 kg/h ormore, for example about 2500 kg/h or more, such as about 2700 kg/h ormore. The cross sectional area of the manifold 144, the cross sectionalarea of the outlet tube 146, and/or the baffle assembly can accommodatehigh electrolyte flow rates and high gas flow rates associated withoperation at high current densities as described herein and provide fora superficial liquid velocity that is about 0.2 m/s or less and a gasflow rate that is about 3 m/s or less so that slug and plug flow areunlikely to develop.

In some examples, the pan assembly can include a baffle assembly insidethe pan assembly, wherein the baffle assembly can reduce or minimize theimpact of high current density and/or fluctuating power dissipation onthe internal temperature profile along the height of the electrolyzercell. The baffle assembly can be suspended in the pan assembly, forexample between a back pan wall and the electrode. In an example, thebaffle assembly includes one or more ribs inside the pan. The one ormore ribs can include one or more notches. A baffle plate comprising oneor more slots can be included and configured to fit onto the one or moreribs such that a corresponding structure of the baffle plate can fitinto the one or more notches of the one or more ribs.

FIGS. 9-15 show several views of a pan assembly 160 that includes anexample baffle assembly 162. Similar to the pan assembly 140 describedabove with respect to FIGS. 3-8 , the pan assembly 160 can be used asthe structure for one or both of the anode half cell 111 and the cathodehalf cell 121 in the electrolyzer cell 100 of FIG. 1 . For example, ifthe pan assembly 160 is used to form part of the anode half cell 111,then the pan assembly 160 can be an anode pan assembly. Similarly, ifthe pan assembly 160 is used to form part of the cathode half cell 121,then the pan assembly 160 can be a cathode pan assembly. Like the panassembly 140, the pan assembly 160 includes a pan 164 (e.g., an anodepan and/or a cathode pan) and an outlet tube 166. The pan assembly 160can also include a manifold 168 through which electrolyte and producedgas can flow before exiting the pan assembly 160 through the outlet tube166, which can be similar or identical to the manifold 144 describedabove with respect to the pan assembly 140. In other words, the panassembly that forms either the anode assembly or the cathode assembly,or both, can include features of both the pan assembly 140 describedabove with respect to FIGS. 3-8 and of the pan assembly 160 describedbelow.

In an example, the baffle assembly 162 of the pan assembly 160 includesa baffle plate 170 that is fitted within the pan 162. In an example, thebaffle plate 170 comprises one or more slots 172 (best seen in FIG. 10). Each slot 172 can interact with a corresponding rib 174 (shown inFIGS. 9, 11, and 12 ), wherein the one or more ribs 174 and the baffleplate 170 form the baffle assembly 162. The baffle plate 170 can haveany number of slots 172 depending on the number of ribs 174 in thebaffle assembly 162. The number of slots can be e.g., from 1 to about200 in the baffle plate 170. The baffle plate 170 can be fitted over theribs 174 in the pan 164. In an example, the one or more ribs 174 areperpendicular or substantially perpendicular to the baffle plate 170 andto the overall orientation of the pan 164. In other words, in anexample, the baffle plate 170 is parallel or substantially parallel to amajor surface of the pan 164, such as a back wall 178 of the pan 164.The electrode 176 associated with the pan assembly 160 (e.g., the anode112 if the pan assembly 160 is an anode pan assembly or the cathode 122if the pan assembly 160 is a cathode pan assembly) can be attached tothe top of the pan assembly 160, e.g., on a side of the baffle assembly162 that is opposite the back wall 178 of the pan 164.

In an example, each of the one or more ribs 174 can include one or morestructures to position the baffle plate 170 relative to the pan 164and/or relative to the electrode 176. In an example, these structuresinclude one or more notches on each rib 174, wherein each notch slidablyengages with a corresponding slot 172 on the baffle plate 170 in orderto position the baffle plate 170 relative to the pan 164, e.g., so thatthe baffle plate 170 is suspended at a specified location relative tothe electrode 176 and/or relative to the back wall 178 of the pan 164,as can be seen in FIGS. 9, 11, and 12 . The notches in the ribs 174 arenot visible in the Figures because the notches have been filled with thebaffle plate 170. The distance of the baffle plate 170 from theelectrode 176 and from the back wall 178 of the pan 164 can be changedby modifying the depth of the notches along the ribs 174.

The positioning of the slots 172 in the baffle plate 170, the length ofthe slots 172, and/or the distance between the slots 172 can affect thefitting of the baffle plate 170 onto the one or more ribs 174. In anexample, the baffle plate 170 is a solid plate with the slots 172 formedtherein, as best seen in FIG. 10 . In other examples, the baffle platecan be an expanded metal plate or a mesh. In an example, the baffleplate 170 is made from a conductive metal, such as, but not limited to,nickel, stainless steel, and the like. In another example, the baffleplate 170 is made from a polymeric material. In either case, the baffleplate 170 can be configured to snap into place using features on theribs 174.

As described earlier, the contribution of internal power dissipation tothe internal temperature distribution within the electrolyzer cell 100can be reduced or minimized through operating conditions such as thetemperature and flow rate of the electrolyte flowing through the halfcells 111, 121 (e.g., through the pan assemblies 160 that form the halfcells 111, 121). High electrolyte flow rates can increase and in someexamples maximize the convective heat transfer within the electrolyzercell 100, thereby helping to reduce or minimize heat buildup and thecorresponding concomitant temperature rise within the cell 100 thatcould otherwise result from the high current densities described herein.As discussed above, operating at high electrolyte flow rates and highcurrent densities can lead to slugging or plug flow at the cell outlet,which can result in pressure fluctuations that can shorten the lifetimeof the membrane 131. The pan assemblies 140, 160 described herein withthe manifold 144 and outlet configurations and/or the baffle assembly162 are designed to reduce or minimize slug and plug flow. Inparticular, the baffle assembly 162 can provide for mixing of theelectrolyte as it flows through the pan assembly 160 to enhanceconvective heat transfer within the electrolyte during electrolysis.

In some examples, the baffle assembly 162 is designed and positioned insuch a way that the gas produced at the electrode 176 can mix with theelectrolyte on the side of the baffle plate 170 closest to the electrode176, resulting in a relatively low density column and defining a risersection. The low density mixture can rise relatively quickly through theriser section. Once above the top of the baffle plate 170, the gas candisengage and flow into the manifold 168 and then into the outlet tube166. A fraction of the electrolyte may then drop back down the side ofthe baffle plate 170 closer to the back wall 178 (i.e., the sideopposite to the electrode 176) of the pan 164 into a down-comer region,thereby creating a circulation loop. This circulation loop (with a risersection 180 on the side of the baffle plate 170 closer to the electrode176 and a down-comer section 182 on the side of the baffle plate 170opposite the electrode 176) that is formed in the pan assembly 160 isillustrated conceptually in FIG. 13 , where it is compared to acomparative pan assembly 184 that does not include a baffle assembly,such as one with a baffle plate like the baffle plate 170, such thatthere is no resulting formation of a circulation pattern. FIG. 14 showsvector plots of a simulated flow distribution of electrolyte in the panassembly 160 with the baffle plate 170 included (left side of FIG. 14 )and a comparative pan assembly 184 without a baffle assembly (right sideof FIG. 14 ). As can be seen in FIG. 14 , without a baffle plate, theelectrolyte solution rises slowly up though the comparative pan assembly184. The gas evolved at the electrode 176 impacts the flow of theelectrolyte, dragging some of the electrolyte up, and buffeting some ofthe electrolyte laterally. Gas lift is evident along the upper left wall(adjacent to the electrode 176) in the comparative pan assembly 184.While the comparative pan assembly 184 without the baffle plate doesresult in the formation of a weak circulation of electrolyte, the panassembly 160 that includes the baffle plate 170 creates a strongcirculation within the pan assembly 160. As is evident from FIG. 14 ,the flow in the riser section 180, e.g., the side of the baffle plate170 closest to the electrode 176, is strongly oriented upward due to gaslift, and the flow on the down-comer section 182, e.g., the side of thebaffle plate 170 closest to the back wall 178 of the pan assembly 160,is strongly oriented downward. The relatively high velocities and shearrates in the riser section 180 help sweep gas from the electrode 176,provide efficient top to bottom mixing within the pan assembly 160, anddrive increased convective cooling.

The baffle assembly 162 can be used to create rapidly flowingcirculation loops so that the electrolyte remains substantiallyisothermal as it flows through the pan assembly 160. Due to the highdegree of top-bottom mixing and circulation, rapid thermal equilibrationof the electrolyte can be achieved as it flows into and through the panassembly 160. Another advantage is that relatively cold electrolyte canbe introduced into the pan assembly 160 which can equilibrate with warmcirculating electrolyte fluid. The circulation rate (or laps of therecirculation loop during electrolyte transit through the pan assembly160) can be anywhere from 1 to 200. The high circulation rate can alsodrive larger shear rates adjacent to the membrane 131, helping to sweepgas away from the membrane 131 and/or enhance or maximize heat transferfrom the membrane 131 to the electrode 176.

The positioning of the baffle plate 170 with respect to the electrode176 as well as to the back wall 178 of the pan 164 and/or the widthWBaffle and length LBaffle of the baffle plate 170 (shown in FIG. 15 ),can affect the velocity of the electrolyte through the riser section 180as well as the down-comer section 182, thereby affecting the circulationrate of the electrolyte within the pan assembly 160. It has been foundthat if the baffle plate 170 is located farther than a specifiedcritical distance from the electrode 176 then the circulation pattern ofthe riser section 180 and the down-comer section 182 may not be formed.Specifically, it has been found that when the gap between the baffleplate 170 and the electrode 176 is too large, free convection of therelatively light, gas-rich zone adjacent to the electrode 176 risesrelatively rapidly compared to the slowly rising electrolyte fartheraway from the electrode 176. The resultant shear forces may drag up someof the electrolyte, which can then fall back down on the side of thebaffle plate 170 closer to the electrode 176 as the gas disengages intothe manifold 168 at the top of the pan assembly 160, resulting in a weakcirculation forming on the side of the baffle plate 170 closest to theelectrode 176. In such a configuration, the baffle plate 170 may notdivide between a riser section and a down-comer section, and a strongcirculation current may not form. If, on the other hand, the baffleplate 170 is too close to the electrode 176, then the space between theelectrode 176 and the baffle plate 170 may fill with gas as the gas isformed at the electrode 176, choking off electrolyte flow in the spacebetween the baffle plate 170 and the electrode 176. A high volumefraction of gas in the space between the baffle plate 170 and theelectrode 176 can result in the membrane and/or the electrode 176masking, and poor electrical and thermal transport.

The depth Dean of the pan 164, the relative depth DBaffle of the baffleplate 170 relative to the electrode 176, the height H_(Baffle) of thebaffle plate 170 relative to the total height Hp_(a)n of the pan 164,and/or the vertical location of the baffle plate 170 within the pan 164(e.g., as dictated by the vertical distance M_(Top) from a top edge ofthe baffle plate 170 to a top wall of the pan 164 and the correspondingvertical distance HBot from a bottom edge of the baffle plate 170 to abottom wall of the pan 164), as illustrated in FIG. 13 , can impact thecirculation pattern of the electrolyte within the pan 164.

In an example, the distance of the baffle plate 170 from the electrode176 (i.e., the relative depth DBaffle of the baffle as illustrated inFIG. 13 ) is from about 5 mm to about 25 mm, for example from about 5 mmto about 15 mm, such as from about 5 mm to about 12 mm, for example fromabout 5 mm to about 10 mm, such as from about 5 mm to about 8 mm, forexample from about 5 mm to about 6 mm, for example from about 6 mm toabout 25 mm, such as from about 6 mm to about 15 mm, for example fromabout 6 mm to about 12 mm, such as from about 6 mm to about 10 mm, forexample from about 6 mm to about 8 mm, for example from about 8 mm toabout 25 mm, such as from about 8 mm to about 15 mm, for example fromabout 8 mm to about 12 mm, for example from about 8 mm to about 10 mm,for example from about 10 mm to about 25 mm, such as from about 10 mm toabout 15 mm, for example from about 10 mm to about 12 mm, such as fromabout 12 mm to about 25 mm, for example from about 12 mm to about 15 mm.In some examples, the distance DBaffle of the baffle plate 170 from theelectrode 176 is equivalent to the depth of the notches on the ribs 174.

In an example, the distance DBaffle from the baffle plate 170 to theelectrode 176 is at from about 0.25 (25%) to about 0.5 (50%) of thetotal depth D_(Pan) of the pan 164, for example from about 0.25 (25%) toabout 0.4 (40%) of the total depth D_(Pan) of the pan 164, such as fromabout 0.25 (25%) to about 0.3 (30%) of the total depth D_(Pan) of thepan 164, for example from about 0.3 (30%) to about 0.5 (50%) of thetotal depth D_(Pan) of the pan 164, such as from about 0.4 (40%) toabout 0.5 (50%) of the total depth D_(Pan) of pan 164.

In an example, the height H_(Baffle) and the positioning of the baffleplate 170 is such that it leaves space at the top (H_(Top) in FIG. 13 )and/or a space at the bottom (H_(Bot) in FIG. 13 ) of the pan 164 forgas and liquid flow. In some examples where the manifold 168 and thebaffle plate 170 both are present in the pan assembly 160, depending onthe depth of the manifold 168 and the placement of the baffle plate 170with respect to the depth D_(Pan) of the pan 164, the baffle plate 170may run behind the manifold 168 (e.g., between the manifold 168 and theelectrode 176) towards the top of the pan 164 or the baffle plate 170may end below the manifold 168. In either case, there can be a spacebetween the baffle plate 170 and the top and/or bottom of the pan 164for gas and liquid flow.

In an example, the space H_(Bot) between a bottom edge of the baffleplate 170 and the bottom wall of the pan 164 is from about 6 mm to about75 mm, for example from about 6 mm to about 65 mm, such as from about 6mm to about 50 mm, for example from about 6 mm to about 40 mm, such asfrom about 6 mm to about 30 mm, for example from about 6 mm to about 20mm, such as from about 6 mm to about 10 mm, for example from about 10 mmto about 75 mm, such as from about 10 mm to about 65 mm, for examplefrom about 10 mm to about 50 mm, such as from about 10 mm to about 40mm, for example from about 10 mm to about 30 mm, such as from about 10mm to about 20 mm, for example from about 10 mm to about 15 mm, such asfrom about 20 mm to about 75 mm, for example from about 20 mm to about65 mm, such as from about 20 mm to about 50 mm, for example from about20 mm to about 40 mm, such as from about 20 mm to about 30 mm, forexample from about 30 mm to about 75 mm, such as from about 30 mm toabout 65 mm, for example from about 30 mm to about 50 mm, such as fromabout 30 mm to about 40 mm, for example from about 40 mm to about 75 mm,such as from about 40 mm to about 65 mm, for example from about 50 mm toabout 75 mm, such as from about 50 mm to about 65 mm, for example fromabout 60 mm to about 75 mm.

In some embodiments, the space H_(Top) between a top edge of the baffleplate 170 and the top wall of the pan 164 or the bottom of the manifold168 is between about 6 mm to about 150 mm, for example from about 6 mmto about 140 mm, such as from about 6 mm to about 130 mm, for examplefrom about 6 mm to about 120 mm, such as from about 6 mm to about 110mm, for example from about 6 mm to about 100 mm, such as from about 6 mmto about 80 mm, for example from about 6 mm to about 70 mm, such as fromabout 6 mm to about 50 mm, for example from about 6 mm to about 25 mm,such as from about 10 mm to about 150 mm, for example from about 10 mmto about 140 mm, such as from about 10 mm to about 130 mm, for examplefrom about 10 mm to about 120 mm, such as from about 10 mm to about 110mm, for example from about 10 mm to about 100 mm, such as from about 10mm to about 80 mm, for example from about 10 mm to about 70 mm, such asfrom about 10 mm to about 50 mm, for example from about 10 mm to about25 mm, such as from about 25 mm to about 150 mm, for example from about25 mm to about 140 mm, such as from about 25 mm to about 130 mm, forexample from about 25 mm to about 120 mm, such as from about 25 mm toabout 110 mm, for example from about 25 mm to about 100 mm, such as fromabout 25 mm to about 80 mm, for example from about 25 mm to about 70 mm,such as from about 25 mm to about 50 mm, for example from about 50 mm toabout 150 mm, such as from about 50 mm to about 140 mm, for example fromabout 50 mm to about 130 mm, such as from about 50 mm to about 120 mm,for example from about 50 mm to about 110 mm, such as from about 50 mmto about 100 mm, for example from about 50 mm to about 80 mm, such asfrom about 50 mm to about 70 mm, for example from about 100 mm to about150 mm, such as from about 100 mm to about 140 mm, for example fromabout 100 mm to about 130 mm, such as from about 100 mm to about 120 mm,for example from about 125 mm to about 150 mm, such as from about 125 mmto about 140 mm, for example from about 130 mm to about 150 mm, such asfrom about 75 mm to about 120 mm. It is to be understood that any ofaforementioned dimensions for the space between the baffle plate andbottom of the anode and/or the cathode pan and the dimensions for thespace between the baffle plate and top of the anode and/or the cathodepan or the bottom of the manifold, may be combined in order to achievethe optimum circulation pattern of the electrolyte.

In some embodiments, the anode and/or the cathode pan assembly providedherein, with the aforementioned manifold and the outlet tube and/or thebaffle assembly provide several advantages such as, but not limited to,accommodating the aforementioned high flow rate of anolyte or catholyteand/or reducing or minimizing the incidence of slug or plug flow;reducing or minimizing large spatial and/or temporal temperaturefluctuations; reducing or minimizing pressure fluctuations due tomultiphase flow in the cell, e.g., to less than 0.5 psi; and/or reducingor minimizing membrane erosion and/or fatigue.

As noted above, operation of the electrolyzer cell at high currentdensities can result in significant challenges, such as, but not limitedto, large amount of heat generated in the cell. In an electrolyzer cellproducing a large amount of gas at high current densities, thegas/electrolyte mixture can have a lower specific heat, a lower density,and/or a lower thermal conductivity than the electrolyte alone.Therefore, the heat removal efficiency of the electrolyte can be reducedas the gas hold up increases. Local temperatures can then rise quicklyif a gas pocket masks a region of the electrode. If a significant regionof the electrode is masked, the unmasked region will have to workharder, increasing the local Joule heating. Local hot spots thusdeveloped can damage the membrane. As the current density is increasedin the cell, power dissipation can also rise dramatically. Large spatialand/or temporal temperature fluctuations can damage the membrane.

FIGS. 16-19 and 20A-20C show an illustrative example of a pan assembly190 that can be used as the anode pan assembly for the anode half cell111 or as the cathode pan assembly for the cathode half cell 121, orboth, in the electrolyzer cell 100 shown in FIG. 1 . The pan assembly190 includes a plurality of ribs 194 with specified geometry and/orspacing, and/or via the use of one or more welds 196 that couple anelectrode 198 of the pan assembly 190 to the ribs 194, wherein the welds196 have a specified weld density and cross-sectional configuration toreduce or minimize power dissipation in order to improve temperaturedistribution during operation of the cell. The pan assembly 190 can alsoinclude features of the pan assembly 140 described above with respect toFIGS. 3-8 (e.g., a manifold and outlet tube through which electrolyteand produced gas can flow before exiting the pan assembly 190, which canbe similar or identical to the manifold 144 and outlet tube 146described above with respect to the pan assembly 140) and/or features ofthe pan assembly 160 described above with respect to FIGS. 9-15 (e.g., abaffle assembly, which can be similar or identical to the baffleassembly 162 described above with respect to the pan assembly 160). Inother words, the pan assembly that forms either the anode assembly orthe cathode assembly, or both, can include features of the pan assembly140 described above with respect to FIGS. 3-8 and/or of the pan assembly160 described above with respect to FIGS. 9-15 in addition to featuresof the pan assembly 190 described below.

The rib geometry, rib spacing, and/or weld density and cross-sectionalconfigurations in the pan assembly 190 can reduce or minimize the effectof one or more of these challenges, such as, but not limited to, by moreeffectively distributing current across the pan assembly 190 to reducethe chance of hot spot formation, reduce or avoid large spatial and/ortemporal temperature fluctuations of the electrolyte along the height ofthe pan assembly 190, and/or reduce or minimize membrane damage due tohot spots.

The design of the pan assembly 190 comprising the one or more ribs 194and the welds 196, as described below, can provide for efficient currentdistribution across the active area of the cell when operating at highcurrent densities. The cross-sectional area of the ribs 194 and thewelds 196 can also allow the cells to be more effective for operationaland economical purposes.

Similar to the pan assemblies 140 and 160 described above with respectto FIGS. 3-15 , the pan assembly 190 can be used as the structure forone or both of the anode half cell 111 and the cathode half cell 121 inthe electrolyzer cell 100 of FIG. 1 , i.e., the pan assembly 190 canform the anode half cell 111 such that the pan assembly 190 is an anodepan assembly and/or the pan assembly 190 can form the cathode half cell121 such that the pan assembly 190 is a cathode pan assembly. The pan192 can include an interior for receiving an electrolyte (i.e., ananolyte if the pan assembly 190 is an anode pan assembly and a catholyteif the pan assembly 190 is a cathode pan assembly) and an electrode 198(i.e., the anode 112 in an anode pan assembly 190 or the cathode 122 isa cathode pan assembly 190). The anode pan assembly and the cathode panassembly can be separated by a separator (i.e., the membrane 131), whichcan be, for example, one or more of a diaphragm, a membrane electrodeassembly (MEA), or an ion exchange membrane (TEM). The pan assembly 190can further comprise components, such as a collection system (e.g., amanifold such as the manifold 144 or 168 described above) that collectsthe gas and the electrolyte for flow out of the pan assembly 190.Various additional separator components can be provided, e.g., toseparate the one or more membranes from the anode, to separate the oneor more membranes from the cathode, to separate one membrane fromanother membrane (e.g., to separate an anion exchange membrane (AEM)from a cation exchange membrane (CEM)), and/or to provide mechanicalintegrity to the one or more membranes. In addition to these components,individual gaskets or gasket tape may be provided in between and alongthe outer perimeter of the components to seal the compartments fromfluid leakage.

In an example, the pan assembly 190 includes a pan 192, one or more ribs194 positioned vertically inside the pan 192, an electrode 198 coupledto the one or more ribs 194, and one or more welds 196 that weld theelectrode 198 to the one or more ribs 194. FIG. 16 is a front view of anillustrative example of the pan assembly 190, FIG. 17 is a sidecross-sectional view of the pan assembly 190, and FIG. 18 is an enlargedview of the cross-section taken along line 18 in FIG. 17 . The Figuresshow the one or more structures that can form the one or more ribs 194.As can be seen particularly in the view of FIG. 18 , in an example, theone or more ribs 194 can be perpendicular or substantially perpendicularto a major dimension of the pan 192. For example, each of the one ormore ribs 194 can be perpendicular or substantially perpendicular to oneor more major faces of the pan 192, such as the electrode 198 or a backpan wall 200.

On top of the pan 192 and on top of the one or more ribs 194 can beplaced the electrode 198. As can be seen, in an example, the electrode198 can be welded to the one or more ribs 194 with one or more welds196. In an example, each of the one or more ribs 194 is coupled to theback wall 200 of the pan 192 by one or more tabs 202 that are coupled tothe back wall 200 with one or more tab welds 204.

In an example, the electrode 198 can be electrically coupled to thesupplied electrical current via the one or more welds 196. Duringoperation of a cell that uses the pan assembly 190 to form the cathodehalf cell, current flows into the cathode (e.g., the electrode 198 ofthe cathode pan assembly 190) through the welds 196 of the cathode panassembly 190. Then, the current flows from the cathode 198 to the one ormore ribs 194 of the cathode pan assembly 190. The current then flowsthrough the one or more ribs 194 of the cathode pan assembly 190 throughthe tabs 202 and finally into a conductor contacting the pan 192 of thecathode pan assembly 190 (e.g., to the anode half cell of an adjacentcell or to a contact plate). During operation of a cell that uses thepan assembly 190 to form the anode half cell, current flows from aconductor contacting the pan 192 of the anode pan assembly 190 (e.g.,from the cathode half cell of an adjacent cell or from a contact plate)to the ribs 194 of the anode pan assembly 190 through the tabs 202, thento the anode (e.g., the electrode 198 of the anode pan assembly 190),and then into a conductor that is electrically connected to one or moreof the welds 196 of the anode pan assembly 190. As noted above, the oneor more ribs 194 can be welded to the back wall 200 of the pan 192 viathe tabs 202 and the tab welds 204. In an example, the tabs 202 set thespacing of the tab welds 204 between the bottom of the ribs 194 and theback wall 200 of the pan 192. Since the current flows between the backwall 200 of the pan 192 and the electrode 198 through the ribs 194, thetabs 202 can provide adequate weld cross-section between the ribs 194and the pan 192. The tabs 202 can facilitate better current distributionacross the active area and provide electrical contact between the ribs194 and the pan 192. However, in other examples, the ribs 194 can bedirectly welded to the back wall 200 of the pan 192 and may not beconnected through tabs.

The geometry and spacing of the one or more ribs 194 can dictate currentflow through the pan assembly 190. The geometry of the ribs 194 caninclude, but not limited to, the number of the ribs 194, the height HRibof the ribs 194, the physical design of the ribs 194, the pitch PRibsbetween adjacent ribs 194, and/or the thickness TRib of the ribs 194 (asshown in FIG. 19 ). As the current flows in through the welds 196, thegeometry, spacing or density, and/or cross-sectional area of the welds196 can also impact current flow through the pan assembly 190. Asincreasingly high currents flow through the cell, the density and thecross sectional area of the welds 196 can significantly impact the localJoule heating and avoid membrane damage from local hot spots. Providedherein are a unique geometry, spacing, and cross-sectional area of theribs 194 as well as the welds 196 that can facilitate efficientoperation of the electrochemical cell made up of one or two of the panassemblies 190 at high current densities.

The physical configuration, i.e., the overall shape, of the one or moreribs 194 can be selected for one or more purposes. For example, one ormore of the ribs 194 can be solid plates, such as solid plates ofconductive metal, such as the example ribs 194A shown in FIG. 20A. Inanother example, the one or more ribs 194 can include one or more holesor openings that allow the electrolyte to move laterally within the pan192, such as the one or more ribs 194B having holes 206 as shown in FIG.20B. In an example, the one or more ribs 194 include one or more notchesfor receiving one or more other structures, such as the ribs 194C shownin FIG. 20C that include one or more notches 208 for receiving portionsof a baffle plate 210 (which is described in more detail below). In anexample, the one or more ribs 194 can include both holes 206 and notches208, as with the ribs 194C shown in FIG. 20C, or can include only theholes 206 or only the notches 208.

The number of ribs 194 inside the pan 192 can impact the currentdistribution and the power dissipation within the pan assembly 190. Inan example, the number of ribs 194 inside the pan 192 is from 1 to 75 ofthe ribs 194, such as from 1 to 60 of the ribs 194, for example from 1to 50 of the ribs 194, such as from 1 to 40 of the ribs 194, for examplefrom 1 to 30 of the ribs 194, such as from 1 to 20 of the ribs 194, suchas from 1 to 10 of the ribs 194, for example from 1 to 5 of the ribs194, such as from 5 to 75 of the ribs 194, for example from 5 to 60 ofthe ribs 194, such as from 5 to 50 of the ribs 194, for example from 5to 40 of the ribs 194, such as from 5 to 30 of the ribs 194, for examplefrom 5 to 20 of the ribs 194, such as from 5 to 10 of the ribs 194, forexample from 10 to 75 of the ribs 194, such as from 10 to 60 of the ribs194, for example from 10 to 50 of the ribs 194, such as from 10 to 40 ofthe ribs 194, for example from 10 to 30 of the ribs 194, such as from 10to 20 of the ribs 194, for example from 20 to 75 of the ribs 194, suchas from 20 to 60 of the ribs 194, for example from 20 to 50 of the ribs194, such as from 20 to 40 of the ribs 194, for example from 20 to 30 ofthe ribs 194, such as from 30 to 75 of the ribs 194, for example from 30to 60 of the ribs 194, such as from 30 to 50 of the ribs 194, forexample from 30 to 40 of the ribs 194, such as from 40 to 75 of the ribs194, for example from 40 to 60 of the ribs 194, such as from 40 to 50 ofthe ribs 194, for example from 50 to 75 of the ribs 194, such as from 50to 60 of the ribs 194, for example from 60 to 75 of the ribs 194. Forexample, the pan assemblies 190 shown in FIGS. 16-19 and 20A-20C showthe pan 192 containing five (5) ribs 194.

A cross-sectional perspective view of the exemplary pan assembly 190 isshown in FIG. 19 . The electrode 198 and the welds 196 are not shown inFIG. 19 . As described above, the pan assembly 190 includes one or moreribs 194 positioned vertically in the pan 192, e.g., the ribs 194 arecoupled to the back wall 200 of the pan 192, such as with the tabs 202,and the ribs 194 extend from the back wall 200 toward the electrode. InFIG. 19 , the pitch, or the distance between, two adjacent ribs 194 islabeled as PRibs, the height of the one or more ribs 194 is labeled asHRib, and the thickness of the one or more ribs 194 is labeled as TRib.The ribs 194 are shown in FIG. 19 as comprising holes 206 for themovement of the electrolyte as well as notches 208. The notches 208facilitate fitting of specified sections of a baffle plate 210 into thespace formed by the notches 208 in order to secure the baffle plate 210to the one or more ribs 194. The baffle plate 210 can be similar oridentical to the baffle plate 170 described above with respect to thepan assembly 160 of FIGS. 9-15 . In an example, the one or more ribs 194are made of a conductive metal, such as, but not limited to, nickel,stainless steel, etc.

It is to be understood that the holes 206 and the notches 208 may not bepresent, e.g., the ribs 194 can each be formed from a solid plate, suchas the ribs 194A of FIG. 20A, or the ribs 194 can have notches 208 butnot have holes 206, or the ribs 194 can have the holes 206 and not thenotches 208. The holes 206, if present, need not be of any specificshape or size. For example, the holes 206 can be circular openings,slits, perforations, or a mesh.

In an example, the length L_(Rib) of the one or more ribs 194 (FIG. 16 )is from about 0.25 meters (m) to about 1.5 m, for example from about0.25 m to about 1.2 m, such as from about 0.25 m to about 1 m, forexample from about 0.25 m to about 0.8 m, such as from about 0.25 m toabout 0.6 m, for example from about 0.25 m to about 0.5 m, such as fromabout 0.25 m to about 0.4 m, for example from about 0.25 m to about 0.3m, such as from about 0.5 m to about 1.5 m, for example from about 0.5 mto about 1.2 m, such as from about 0.5 m to about 1 m, for example fromabout 0.5 m to about 0.8 m, such as from about 0.5 m to about 0.6 m, forexample from about 0.6 m to about 1.5 m, such as from about 0.6 m toabout 1.2 m, for example from about 0.6 m to about 1 m, such as fromabout 0.6 m to about 0.8 m, for example from about 0.7 m to about 1.5 m,such as from about 0.7 m to about 1.2 m, for example from about 0.7 m toabout 1 m, such as from about 0.7 m to about 0.8 m, for example fromabout 0.8 m to about 1.5 m, such as from about 0.8 m to about 1.2 m, forexample from about 0.8 m to about 1 m.

In an example, the length of the notch 208 in each of the one or moreribs 194 is from about 5 millimeters (mm) to about 100 mm, for examplefrom about 5 mm to about 80 mm, such as from about 5 mm to about 60 mm,for example from about 5 mm to about 50 mm, such as from about 5 mm toabout 40 mm, for example from about 5 mm to about 30 mm, such as fromabout 5 mm to about 20 mm, for example from about 5 mm to about 10 mm,such as from about 10 mm to about 100 mm, for example from about 10 mmto about 50 mm, such as from about 10 mm to about 40 mm, for examplefrom about 10 mm to about 30 mm, such as from about 10 mm to about 20mm, for example from about 20 mm to about 100 mm, such as from about 20mm to about 50 mm, for example from about 20 mm to about 40 mm, such asfrom about 20 mm to about 30 mm, for example from about 30 mm to about100 mm, such as from about 30 mm to about 50 mm, for example from about30 mm to about 40 mm, such as from about 40 mm to about 100 mm, forexample from about 40 mm to about 50 mm, such as from about 50 mm toabout 100 mm, for example from about 75 mm to about 100 mm.

In an example, the thickness T_(Rib) of the one or more ribs 194 is fromabout 1 mm to about 3 mm, for example from about 1 mm to about 2.5 mm,such as from about 1 mm to about 2 mm, for example from about 1 mm toabout 1.5 mm, such as from about 2 mm to about 3 mm, for example fromabout 2 mm to about 2.5 mm, such as from about 2.5 mm to about 3 mm.

In an example, the height HRth of the one or more ribs 194 is from about10 mm to about 110 mm, for example from about 10 mm to about 100 mm,such as from about 10 mm to about 75 mm, for example from about 10 mm toabout 70 mm, such as from about 10 mm to about 60 mm, for example fromabout 10 mm to about 50 mm, such as from about 10 mm to about 40 mm, forexample from about 10 mm to about 30 mm, such as from about 20 mm toabout 110 mm, for example from about 20 mm to about 75 mm, such as fromabout 20 mm to about 70 mm, for example from about 20 mm to about 60 mm,such as from about 20 mm to about 50 mm, for example from about 20 mm toabout 40 mm, such as from about 20 mm to about 30 mm, for example fromabout 30 mm to about 110 mm, such as from about 30 mm to about 75 mm,for example from about 30 mm to about 70 mm, such as from about 30 mm toabout 60 mm, for example from about 30 mm to about 50 mm, such as fromabout 30 mm to about 40 mm, for example from about 40 mm to about 110mm, such as from about 40 mm to about 75 mm, for example from about 40mm to about 70 mm, such as from about 40 mm to about 60 mm, for examplefrom about 40 mm to about 50 mm, such as from about 50 mm to about 110mm, for example from about 50 mm to about 75 mm, such as from about 50mm to about 70 mm, for example from about 50 mm to about 60 mm, such asfrom about 60 mm to about 110 mm, for example from about 60 mm to about75 mm, such as from about 70 mm to about 110 mm, for example from about70 mm to about 80 mm.

In an example, the pitch PRths between two adjacent ribs 194 is fromabout 40 mm to about 200 mm, for example from about 40 mm to about 150mm, such as from about 40 mm to about 140 mm, for example from about 40mm to about 130 mm, such as from about 40 mm to about 120 mm, forexample from about 40 mm to about 110 mm, such as from about 40 mm toabout 100 mm, for example from about 40 mm to about 80 mm, such as fromabout 40 mm to about 70 mm, for example from about 60 mm to about 200mm, such as from about 60 mm to about 150 mm, for example from about 60mm to about 140 mm, such as from about 60 mm to about 130 mm, forexample from about 60 mm to about 120 mm, such as from about 60 mm toabout 110 mm, for example from about 60 mm to about 100 mm, such as fromabout 60 mm to about 80 mm, for example from about 80 mm to about 200mm, such as from about 80 mm to about 150 mm, for example from about 80mm to about 100 mm, such as from about 100 mm to about 200 mm, forexample from about 100 mm to about 150 mm, such as from about 100 mm toabout 140 mm, for example from about 100 mm to about 130 mm, such asfrom about 100 mm to about 120 mm, for example from about 125 mm toabout 200 mm, such as from about 125 mm to about 150 mm, for examplefrom about 125 mm to about 140 mm, such as from about 130 mm to about150 mm, for example from about 75 mm to about 120 mm.

As shown in FIGS. 18 and 20A-20C, the electrode 198 can be welded to thetop of the one or more ribs 194 with a plurality of welds 196. In anexample, the electrode 198 is a planar electrode or an expanded metal ora mesh. In examples where the electrode 198 is an expanded metal or amesh, the thickness of each strand that forms the mesh can be from about0.5 mm to about 3 mm, for example from about 0.5 mm to about 2.5 mm,such as from about 0.5 mm to about 2 mm, for example from about 0.5 mmto about 1.5 mm, such as from about 0.5 mm to about 1 mm, for examplefrom about 1 mm to about 3 mm, such as from about 1 mm to about 2.5 mm,for example from about 1 mm to about 2 mm, such as from about 1 mm toabout 1.5 mm, for example from about 1.5 mm to about 3 mm, such as fromabout 1.5 mm to about 2.5 mm, for example from about 1.5 mm to about 2mm, such as from about 2 mm to about 3 mm, for example from about 2.5 mmto about 3 mm.

The geometry, spacing, density, and/or cross-sectional area of the welds196 can impact current flow through the pan assembly 190. As theoperational current density is increased and more current flows throughthe cell, the density of the welds 196 (e.g., the cross-sectional areaof the welds 196 and the spacing between welds 196) can impact the localJoule heating. The density of the welds 196 can be selected to reducethe or minimize the chances of membrane damage due to the formationlocal hot spots. The example welds 196 in FIGS. 20A-20C are illustratedas spots. However, the welds 196 can be in form of lines, spots,patterns, or any other shape, or combinations thereof. For example, aspot welder can form the welds 196 as spots, while a laser welder canproduce the welds 196 as lines and/or spots and/or patterns. Patternsthat the welds 196 can be formed as include, but are not limited to, acombination of dots, an array of dots, dashes, spots, lines, and linesegments, which can be arranged in the pattern of any geometricallyregular shape, such as a generally rectangular geometry, a generallycircular geometry, or a generally hexagonal geometry, or can be arrangedin an irregular shape.

Examples of welding techniques that can be used to form the welds 196include, but are not limited to: laser welding, TiG welding, and spotwelding, for example resistance spot welding. Laser welding may enable asingle linear weld 196 along a substantial portion of the length LRib ofone of the ribs 194 up to and including the entire length LRib of therib 194 in order to weld the rib 194 to the electrode 198. For example,when the one or more ribs 194 are a solid plate (e.g., ribs 194A of FIG.20A) or a plate with holes that does not include notches 208 (e.g., theribs 194B of FIG. 20B), there may be a single linear weld 196 along thewhole length LRib of the rib 194 in order to join the rib 194 to theelectrode 198. Laser welding or TiG welding may also be used to createwelds 196 in the form of line segments. For example, when the one ormore of the ribs 194 include notches 208 (e.g., the ribs 194C of FIG.20C), there may be segments of weld lines over the portions of the ribs194 that come into contact with the electrode 198, but not over thenotches 208. Laser welding can also produce weld patterns comprisingdots, an array of dots, dashes, spots, line segments, long lines, andany specified geometry, such as an oval geometry, rectangular geometry,circular geometry, hexagonal geometry, or combinations thereof. The weldgeometries may be dictated by the shape of the welding tip and anvil,such as when the welds are created with resistance welding. TiG weldsmay be created manually, and can be in arbitrary form.

In an example, the geometry of the welds 196 includes the number ofwelds in the pan 192. The number of the welds 196 coupling the electrode198 to the ribs 194 can impact the current distribution and the powerdissipation within the pan assembly 190. In an example, the number ofwelds 196 per rib 194 that are in the form of the spots (such as theexample spot welds 196 shown in FIGS. 18 and 20A-20C) is from 10 to 50of the welds 196 per rib 194, for example from 10 to 40 of the welds 196per rib 194, such as from 10 to 30 of the welds 196 per rib 194, forexample from 10 to 20 of the welds 196 per rib 194, such as from 20 to50 of the welds 196 per rib 194, for example from 20 to 40 of the welds196 per rib 194, such as from 20 to 30 of the welds 196 per rib 194, forexample from 30 to 40 of the welds 196 per rib 194, such as from 35 to40 of the welds 196 per rib 194, for example from 40 to 50 of the welds196 per rib 194.

In an example, the distance between the welds 196 when in the form ofspot welds is from about 25 mm to about 200 mm, for example from about25 mm to about 150 mm, such as from about 25 mm to about 100 mm, forexample from about 25 mm to about 75 mm, such as from about 25 mm toabout 50 mm, for example from about 50 mm to about 200 mm, such as fromabout 50 mm to about 150 mm, for example from about 50 mm to about 100mm, such as from about 50 mm to about 75 mm, for example from about 75mm to about 200 mm, such as from about 75 mm to about 150 mm, forexample from about 75 mm to about 100 mm, such as from about 100 mm toabout 200 mm, for example from about 100 mm to about 150 mm,independently in x- and y-directions.

In an example, the number of the welds 196 per rib 194 that are in theform of line welds or line segment welds is between 1 to 75 of the welds196 per rib 194, for example from 1 to 70 of the welds 196 per rib 194,such as from 1 to 60 of the welds 196 per rib 194, for example from 1 to50 of the welds 196 per rib 194, such as from 1 to 40 of the welds 196per rib 194, for example from 1 to 30 of the welds 196 per rib 194, suchas from 1 to 20 of the welds 196 per rib 194, for example from 1 to 10of the welds 196 per rib 194, such as from 2 to 75 of the welds 196 perrib 194, for example from 2 to 70 of the welds 196 per rib 194, such asfrom 2 to 60 of the welds 196 per rib 194, for example from 2 to 50 ofthe welds 196 per rib 194, such as from 2 to 40 of the welds 196 per rib194, for example from 2 to 30 of the welds 196 per rib 194, such as from2 to 20 of the welds 196 per rib 194, for example from 2 to 10 of thewelds 196 per rib 194, such as from 10 to 75 of the welds 196 per rib194, for example from 10 to 70 of the welds 196 per rib 194, such asfrom 10 to 60 of the welds 196 per rib 194, for example from 10 to 50 ofthe welds 196 per rib 194, such as from 10 to 40 of the welds 196 perrib 194, for example from 10 to 30 of the welds 196 per rib 194, such asfrom 10 to 20 of the welds 196 per rib 194, for example from 25 to 75 ofthe welds 196 per rib 194, such as from 25 to 50 of the welds 196 perrib 194, for example from 50 to 75 of the welds 196 per rib 194, such asfrom 60 to 75 of the welds 196 per rib 194.

In an example, the distance between the welds 196 when in the form ofthe line welds or line segment welds is from about 40 mm to about 200mm, for example from about 40 mm to about 150 mm, such as from about 40mm to about 100 mm, for example from about 40 mm to about 75 mm, such asfrom about 75 mm to about 200 mm, for example from about 75 mm to about150 mm, such as from about 75 mm to about 100 mm, for example from about100 mm to about 200 mm, such as from about 100 mm to about 150 mm, forexample from about 150 mm to about 200 mm, independently in x- andy-directions.

In an example, when the one or more ribs 194 comprise the one or morenotches 208 and the welds 196 comprise one or more line segments thatweld the electrode 198 to the ridges of the ribs 194 formed betweennotches 208, the line segment of a particular weld 196 can run along theentire length of a ridge between notches 208 or along only a partiallength of a ridge between notches 208. In an example, the length of aline segment weld 196 is the length of the ridge between notches 208 orthe length of the line segment weld 196 is from about 0.25 m to about 1m, for example from about 0.25 m to about 0.8 m, such as from about 0.25m to about 0.6 m, for example from about 0.25 m to about 0.5 m, such asfrom about 0.25 m to about 0.4 m, for example from about 0.25 m to about0.3 m, such as from about 0.5 m to about 1 m, for example from about 0.5m to about 0.8 m, such as from about 0.5 m to about 0.6 m, for examplefrom about 0.6 m to about 1 m, such as from about 0.6 m to about 0.8 m,for example from about 0.7 m to about 1 m, such as from about 0.7 m toabout 0.8 m, for example from about 0.8 m to about 1 m.

In an example, the distance between two adjacent line segment welds 196is from about 5 mm to about 100 mm, for example from about 5 mm to about80 mm, such as from about 5 mm to about 60 mm, for example from about 5mm to about 50 mm, such as from about 5 mm to about 40 mm, for examplefrom about 5 mm to about 30 mm, such as from about 5 mm to about 20 mm,for example from about 5 mm to about 10 mm, such as from about 10 mm toabout 100 mm, for example from about 10 mm to about 50 mm, such as fromabout 10 mm to about 40 mm, for example from about 10 mm to about 30 mm,such as from about 10 mm to about 20 mm, for example from about 20 mm toabout 100 mm, such as from about 20 mm to about 50 mm, for example fromabout 20 mm to about 40 mm, such as from about 20 mm to about 30 mm, forexample from about 30 mm to about 100 mm, such as from about 30 mm toabout 50 mm, for example from about 30 mm to about 40 mm, such as fromabout 40 mm to about 100 mm, for example from about 40 mm to about 50mm, such as from about 50 mm to about 100 mm, for example from about 75mm to about 100 mm.

In example, the cross-sectional area of each weld 196 is from about 6square millimeters (mm²) to about 3300 mm², for example from about 6 mm²to about 3000 mm², such as from about 6 mm² to about 2000 mm², forexample from about 6 mm² to about 1000 mm², such as from about 6 mm² toabout 500 mm², for example from about 6 mm² to about 300 mm², such asfrom about 6 mm² to about 100 mm², for example from about 50 mm² toabout 3300 mm², such as from about 50 mm² to about 3000 mm², for examplefrom about 50 mm² to about 2000 mm², such as from about 50 mm² to about1000 mm², for example from about 50 mm² to about 500 mm², such as fromabout 50 mm² to about 300 mm², for example from about 50 mm² to about100 mm², such as from about 100 mm² to about 3300 mm², for example fromabout 100 mm² to about 3000 mm², such as from about 100 mm² to about2000 mm², for example from about 100 mm² to about 1000 mm², such as fromabout 100 mm² to about 500 mm², for example from about 100 mm² to about300 mm², such as from about 500 mm² to about 3300 mm², for example fromabout 500 mm² to about 3000 mm², such as from about 500 mm² to about2000 mm², for example from about 500 mm² to about 1000 mm², such as fromabout 1000 mm² to about 3300 mm², for example from about 1000 mm² toabout 3000 mm², such as from about 1000 mm² to about 2000 mm², forexample from about 2000 mm² to about 3000 mm², such as from about 2500mm² to about 3000 mm².

In an example, the geometry, spacing or density, and/or cross-sectionalarea of the welds 196 is such that a ratio of the cross-sectional areaof the electrode 198 relative to the total cross-sectional area of thewelds 196 is from about 15:1 to about 2000:1, for example from about15:1 to about 1000:1, such as from about 15:1 to about 500:1.

In an example, the geometry, spacing or density, and/or cross-sectionalarea of the welds 196 is such that the current density through each weld196 when the cell 190 is operating at its maximum current density isabout 20 amps per square millimeter (A/mm²) or less, for example about19 A/mm² or less, such as 18 A/mm² or less, for example about 17 A/mm²or less, such as about 16 A/mm² or less, for example about 15 A/mm² orless, such as about 14 A/mm² or less, for example about 13 A/mm² orless, such as about 12.5 A/mm² or less, for example about 12 A/mm² orless, such as about 11 A/mm² or less, for example about 10 A/mm² orless, such as about 9 A/mm² or less, for example about 8 A/mm² or less,or from about 5 A/mm² to about 20 A/mm², such as from about 7.5 A/mm² toabout 15 A/mm², for example from about 7.5 A/mm² to about 10 A/mm².

In one specific and non-limiting example, the welds 196 are in the formof spot welds and there are from 10 to 50 of the welds 196 per rib 194,the distance between adjacent spot welds 196 is from about 25 mm toabout 200 mm (independently in the x- and y-directions), thecross-sectional area of each spot weld 196 is from about 6 mm² to about3300 mm², and the current density through each spot weld 196 is 6 A/mm²or less, for example 4 A/mm² or less. In another specific andnon-limiting example, the welds 196 are in the form of line welds andthere from 1 to 75 of the welds 196 per rib 194, the distance betweenadjacent line welds 196 is from about 40 mm to about 200 mm(independently in the x- and y-directions), the cross-sectional area ofeach line weld 196 is from about 6 mm² to about 3300 mm², and thecurrent density through each line weld 196 is 6 A/mm² or less, forexample 4 A/mm² or less.

In an example, an electrochemical cell 100 comprising a pan assemblywith one or any combination of the structures described above for thepan assemblies 140, 160, 190 for one or both of the anode half cell 111and the cathode half cell 121 can operate at a current density of fromabout 300 mA/cm² to about 6000 mA/cm², for example from about 300 mA/cm²to about 5000 mA/cm², such as from about 300 mA/cm² to about 4000mA/cm², for example from about 300 mA/cm² to about 3000 mA/cm², such asfrom about 300 mA/cm² to about 2000 mA/cm², for example from about 300mA/cm² to about 1000 mA/cm², such as from about 300 mA/cm² to about 800mA/cm², for example from about 300 mA/cm² to about 600 mA/cm², such asfrom about 300 mA/cm² to about 500 mA/cm², for example from about 500mA/cm² to about 6000 mA/cm², such as from about 500 mA/cm² to about 5000mA/cm², for example from about 500 mA/cm² to about 4000 mA/cm², such asfrom about 500 mA/cm² to about 3000 mA/cm², for example from about 500mA/cm² to about 2000 mA/cm², such as from about 500 mA/cm² to about 1000mA/cm², for example from about 500 mA/cm² to about 800 mA/cm², such asfrom about 500 mA/cm² to about 600 mA/cm², for example from about 600mA/cm² to about 6000 mA/cm², such as from about 600 mA/cm² to about 5000mA/cm², for example from about 600 mA/cm² to about 4000 mA/cm², such asfrom about 600 mA/cm² to about 3000 mA/cm², for example from about 600mA/cm² to about 2000 mA/cm², such as from about 600 mA/cm² to about 1000mA/cm², for example from about 600 mA/cm² to about 800 mA/cm², such asfrom about 800 mA/cm² to about 6000 mA/cm², for example from about 800mA/cm² to about 5000 mA/cm², such as from about 800 mA/cm² to about 4000mA/cm², for example from about 800 mA/cm² to about 3000 mA/cm², such asfrom about 800 mA/cm² to about 2000 mA/cm², for example from about 800mA/cm² to about 1000 mA/cm², such as from about 1000 mA/cm² to about6000 mA/cm², for example from about 1000 mA/cm² to about 5000 mA/cm²,such as from about 1000 mA/cm² to about 4000 mA/cm², for example fromabout 1000 mA/cm² to about 3000 mA/cm², such as from about 1000 mA/cm²to about 2000 mA/cm², for example from about 2000 mA/cm² to about 6000mA/cm², such as from about 2000 mA/cm² to about 5000 mA/cm², for examplefrom about 2000 mA/cm² to about 4000 mA/cm², such as from about 2000mA/cm² to about 3000 mA/cm², for example from about 3000 mA/cm² to about6000 mA/cm², such as from about 3000 mA/cm² to about 5000 mA/cm², forexample from about 3000 mA/cm² to about 4000 mA/cm², such as from about4000 mA/cm² to about 6000 mA/cm², for example from about 4000 mA/cm² toabout 5000 mA/cm², such as from about 5000 mA/cm² to about 6000 mA/cm².In some examples, an electrochemical cell 100 comprising any one of thepan assemblies 140, 160, 190 for one or both of the anode half cell 111and the cathode half cell 121 operates at high current densities of fromabout 300 mA/cm² to about 3000 mA/cm², such as from about 300 mA/cm² toabout 2000 mA/cm², for example from about 300 mA/cm² to about 1000mA/cm², such as from about 300 mA/cm² to about 800 mA/cm², for examplefrom about 300 mA/cm² to about 600 mA/cm², such as from about 300 mA/cm²to about 500 mA/cm² for example from about 300 mA/cm² to about 400mA/cm^(2.)

In an example, a pan assembly comprising one or any combination of thestructures described above for the pan assemblies 140, 160, 190 canaccommodate a high flow rate of electrolyte (either anolyte through ananode pan assembly or catholyte through a cathode pan assembly), forexample from about 200 kilograms per hour (kg/h) to about 10,000 kg/h,such as from about 200 kg/h to about 9000 kg/h, for example from about200 kg/h to about 8000 kg/h, such as from about 200 kg/h to about 7000kg/h, for example from about 200 kg/h to about 6000 kg/h, such as fromabout 200 kg/h to about 5000 kg/h, for example from about 200 kg/h toabout 4000 kg/h, such as from about 200 kg/h to about 3000 kg/h, forexample from about 200 kg/h to about 2000 kg/h, such as from about 200kg/h to about 1000 kg/h, for example from about 500 kg/h to about 10,000kg/h, such as from about 500 kg/h to about 9000 kg/h, for example fromabout 500 kg/h to about 8000 kg/h, such as from about 500 kg/h to about7000 kg/h, for example from about 500 kg/h to about 6000 kg/h, such asfrom about 500 kg/h to about 5000 kg/h, for example from about 500 kg/hto about 4000 kg/h, such as from about 500 kg/h to about 3000 kg/h, forexample from about 500 kg/h to about 2000 kg/h, such as from about 500kg/h to about 1000 kg/h, for example from about 800 kg/h to about 10,000kg/h, such as from about 800 kg/h to about 9000 kg/h, for example fromabout 800 kg/h to about 8000 kg/h, such as from about 800 kg/h to about7000 kg/h, for example from about 800 kg/h to about 6000 kg/h, such asfrom about 800 kg/h to about 5000 kg/h, for example from about 800 kg/hto about 4000 kg/h, such as from about 800 kg/h to about 3000 kg/h, forexample from about 800 kg/h to about 2000 kg/h, such as from about 800kg/h to about 1000 kg/h, for example from about 1000 kg/h to about10,000 kg/h, such as from about 1000 kg/h to about 9000 kg/h, forexample from about 1000 kg/h to about 8000 kg/h, such as from about 1000kg/h to about 7000 kg/h, for example from about 1000 kg/h to about 6000kg/h, such as from about 1000 kg/h to about 5000 kg/h, for example fromabout 1000 kg/h to about 4000 kg/h, such as from about 1000 kg/h toabout 3000 kg/h, for example from about 1000 kg/h to about 2000 kg/h,such as from about 3000 kg/h to about 10,000 kg/h, for example fromabout 3000 kg/h to about 9000 kg/h, such as from about 3000 kg/h toabout 8000 kg/h, for example from about 3000 kg/h to about 7000 kg/h,such as from about 3000 kg/h to about 6000 kg/h, for example from about3000 kg/h to about 5000 kg/h, such as from about 5000 kg/h to about10,000 kg/h, for example from about 5000 kg/h to about 8000 kg/h, suchas from about 5000 kg/h to about 6000 kg/h, for example from about 6000kg/h to about 10,000 kg/h, such as from about 6000 kg/h to about 8000kg/h, for example from about 8000 kg/h to about 10,000 kg/h.

In an example, a pan assembly comprising one or any combination of thestructures described above for the pan assemblies 140, 160, 190 canprovide for a superficial liquid velocity of the electrolyte through thepan assembly 140, 160, 190 of 0.1 m/s or less, for example 0.08 m/s orless, such as 0.05 m/s or less, for example 0.01 m/s or less.

Temperature Control

Control of the temperature within the electrochemical cell can beimportant for operation of the cell. In operation, the current densitythrough the cell can be varied often, for instance to take advantage ofpower price fluctuations (as described below). To maximize performanceand the lifetime of the separator, it is generally preferred to maintainthe separator within a small range of temperatures. If the temperaturesof the electrolyte inlets into the electrochemical cell is held constantor substantially constant while the current density is changedsignificantly, the temperature at the separator will vary significantly.

The inventors have discovered that the flow rates of electrolyte throughthe anode half cell and the cathode half cell of the electrochemicalcell 100 can be set so that the resulting temperature of the electrolyteoutlet streams can be maintained within a specified range at the highestexpected operational current density using convenient temperatures forthe inlet streams. FIG. 21 shows an example electrochemical cell 300that is configured for temperature control to maintain a temperature ofa separator 331 within the cell 300. The cell 300 is similar to theexample cell 100 described above with respect to FIG. 1 . For example,like the cell 100, the electrochemical cell 300 comprises two halfcells: a first half cell 311 and a second half cell 321. In an example,the first and second half cells 311, 321 are separated by a separator331, such as a membrane 331.

The first half cell 311 can comprise a first electrode 312, which can beplaced proximate to the separator 331, and the second half cell 321 cancomprise a second electrode 322, which can be placed proximate to theseparator 331, for example on an opposite side of the separator 331 fromthe first electrode 312. In an example, the first electrode 312 is theanode for the cell 300 and the second electrode 322 is the cathode forthe cell 300, such that the first half cell 311 may also be referred toas the anode half cell 311, the first electrode 312 may also be referredto as the anode 312, the second half cell 321 may also be referred to asthe cathode half cell 321, and the second electrode 322 may also bereferred to as the cathode 322. Each of the electrodes 312, 322 can becoated with one or more electrocatalysts to speed the reaction towardthe hydrogen gas (H₂ gas) and/or the oxygen gas (O₂ gas), such as, butare not limited to, highly dispersed metals or alloys of platinum groupmetals, such as platinum, palladium, ruthenium, rhodium, iridium, ortheir combinations such as platinum-rhodium, platinum-ruthenium, ornickel mesh coated with ruthenium oxide (RuO₂).

The anode 312 can be electrically connected to an external positiveconductor 316 and the cathode 322 can be electrically connected to anexternal negative conductor 326. When the separator 331 is wet and is inelectrolytic contact with the electrodes 312 and 322, and an appropriatevoltage is applied across the conductors 316 and 326, O₂ gas isliberated at the anode 312 or H₂ gas is liberated at the cathode 322, orboth. In certain configurations, an electrolyte, e.g., one comprising ofa solution of KOH in water, is fed into the half cells 311, 321. Forexample, the electrolyte can flow into the anode half cell 311 through afirst electrolyte inlet 314 and into the cathode half cell 321 through asecond electrolyte inlet 324. In an example, the flow of the electrolytethrough the anode half cell 311 can pick up produced O₂ gas as bubbles313, which exit the anode half cell 311 through a first outlet 315.Similarly, the flow of the electrolyte through the cathode half cell 321can pick up produced H₂ gas as bubbles 323, which can exit the cathodehalf cell 321 through a second outlet 325.

By referring to a lookup table an operator can set the temperatures ofthe inlet streams 314, 324 as a function of the current density at whichthe cell 300 is currently being run such that the resulting temperaturesof the outlet streams 315, 325 does not fluctuate significantly, e.g.,so that the temperatures of the outlet streams 315, 325 are within aspecified temperature variance of a target temperature. In anotherexample, the temperature of the inlet streams 314, 324 can be varied inorder to maintain a temperature of the separator 331 at a constant orsubstantially constant set point (which can be determined by measuringthe temperatures of one or both of the outlet streams 325, 315 andcalculating the temperature of the separator 331 based on one or more ofthe temperature of the outlet stream(s) 315, 325 and the operatingcurrent density). In an example, the inlet temperature control isautomated through one or more controllers 340, 342 (e.g., a firstcontroller 340 configured for temperature control of the first inletstream 314 and a second controller 342 configured for temperaturecontrol of the second outlet stream 324 based on temperature of thesecond outlet stream 325), such as a programmable logic controller(“PLC”). The temperature control can be linked to one or more of: thecurrent density setting (e.g., the current across the electrolyzer cell300 per area of the electrodes 312, 322), the voltage across theelectrolyzer cell 300, and the temperature of the corresponding outletstream 315, 325. In some examples, the temperature control can beautomated using a proportional-integral-derivative (“PID”) controller,or a feed-forward control scheme, or both. In an example, the inlettemperature control is controlled via a feed-forward control based on acurrent density setpoint and the observed voltage across theelectrolyzer cell 300. In another example, in addition to thefeed-forward control by current density, the temperature of thecorresponding electrolyte outlet 315, 325 can also be used to controlthe temperature of the inlet 314, 324 via a PID controller tuned forslow response, which can allow the temperature of the outlet 315, 325 tofine tune the temperature of the inlet 314, 324, after a fast responsefrom the feed-forward controller.

In an example, shown in FIG. 21 , control of the temperatures of theinlet stream 314, 324 is effectively accomplished using a mixing schemewith a cooling heat exchanger 344, 346 that can cool at least a portionof the hot electrolyte return as it flows from the electrolyte outlet315, 325 to the corresponding electrolyte inlet 314, 315. In the exampleof FIG. 21 , a first cooling heat exchanger 344 is configured forcooling electrolyte of the first outlet stream 315 exiting the anodehalf cell 311 before it is recycled to the first inlet stream 314. Asimilar second cooling heat exchanger 346 is configured for coolingelectrolyte of the second outlet stream 325 exiting the cathode halfcell 321 before it is recycled to the second inlet stream 324. In anexample, the electrolyte recycling configuration can include a bypassline 350, 352 that is configured to allow some or all of the recyclingelectrolyte to bypass the cooling heat exchanger 344, 346 (e.g., a firstbypass line 350 to bypass the first cooling heat exchanger 344 and asecond bypass line 352 to bypass the second cooling heat exchanger 346)so that the bypassing portion of the electrolyte is not cooled andremains at or near the hot temperature at the electrolyte outlet 315,325. A corresponding bypass control valve 354, 356 can be included tomodulate the proportion of recycling electrolyte that flows through thecooling heat exchanger 344, 346 and the proportion that will flowthrough the bypass line 350, 352 (e.g., a first control valve 354 tomodulate flow through the first cooling heat exchanger 344 and the firstbypass line 350 and a second control valve 356 to modulate flow throughthe second cooling heat exchanger 346 and the second bypass line 352).In the example shown in FIG. 21 , the bypass control valves 354, 356 aresituation on the bypass lines 350, 352. However, those having skill inthe art will appreciate that the control valve(s) can be positioned atthe inlet line feeding into the cooling heat exchangers 344, 346 or atthe outlet line exiting the cooling heat exchangers 344, 346, whichwould still achieve the same effect of modulating the proportion of theelectrolyte that flows through the heat exchangers 344, 346 and thebypass lines 350, 352.

The streams flowing through the cooling heat exchanger 344, 346 and thebypass line 350, 352 are then mixed to achieve a specified set-pointtemperature. For example, if it is desired that the temperature of theelectrolyte fed to the cell 300 via the inlet 314, 324 be higher thanits current temperature, then the control valve 354, 356 can becontrolled so that a lower proportion of the electrolyte flows throughthe cooling heat exchanger 344, 346 relative to the proportion of theelectrolyte that flows through the bypass line 350, 352 so that arelatively smaller amount of the electrolyte is cooled by the coolingheat exchanger 344, 346, and thus so that the temperature of theelectrolyte after mixing the two streams is higher. Similarly, if it isdesired that the temperature of the electrolyte fed to the cell 300 belower than its current temperature, then the control valve 354, 356 canbe controlled so that a higher proportion of the electrolyte flowsthrough the cooling heat exchanger 344, 346 relative to the proportionthat flows through the bypass line 350, 352 so that a relatively higheramount of the electrolyte is cooled by the cooling heat exchanger 344,346, and thus so that the temperature of the electrolyte after mixingthe two streams is lower.

In an example, a flow control valve 360, 362 located downstream of themixing point can ensure that a feed flow rate of the electrolyte to theinlet 314, 324 remains constant or substantially constant (e.g., a firstflow control valve 360 to control the flow rate of electrolyte to thefirst inlet 314 and a second flow control valve 362 to control the flowrate of electrolyte to the second inlet 324). In another example (notshown), a temperature control valve (similar to the control valve 354,356 in FIG. 21 ) can control the flow rate through the cooling heatexchanger 344, 346 and a flow control valve can control the flow ratethrough the heat exchanger bypass line 350, 352. In an example, thecooling heat exchanger 344, 346 is at least slightly oversized (in termsof the flow rate that the heat exchanger 344, 346 can accommodate or theheat exchange capacity of the heat exchanger 344, 346), so that thecombination of the cooling heat exchanger 344, 346 and the bypass line350, 352 can provide for adequate temperature control and flow control.The inventors have found that this type of temperature control for theelectrolyte inlet stream 314, 324 can provide for fast and linear orsubstantially linear inlet temperature control, compared to controllingthe temperature of the inlet stream 314, 324 by changing the amount ofcooling water being fed to the cooling heat exchanger 344, 346.

The combination of a fast linear temperature control of the inlet 314,324 with a feed-forward controller setting the inlet temperature setpoint based on current density or observed voltage across the cell 300,or both, can provide for stable temperature control for the outletstream 315, 325 when changing the current density (e.g., when changingthe current density being applied across the cell 300 in order to changethe H₂ production rate to account for changes in electricity pricing, asdescribed in more detail below). Rapid temperature management in thisway can compensate for quick changes of current density while minimizingthermal shock to the separator 331, the electrodes 312, 322, and othercomponents of the cell 300.

Dynamic Cell Operation for Improved Overall Operating Expense

The various structural aspects of the electrolyzer cells and othersupporting apparatus described above—i.e., the manifold 144 and outlettube 146 configuration of the example pan assembly 140 to accommodate ahigh gas production rate and a high electrolyte flow rate (as describedabove with respect to FIGS. 3-8 ); the baffle plate assembly 162 of theexample pan assembly 160 to further accommodate the high gas productionrate and high electrolyte flow rate and to assist in temperaturedistribution within the electrolyte flowing through the pan assembly (asdescribed above with respect to FIGS. 9-15 ); the ribs 194 and welds 196for coupling the electrode 198 to the ribs 194 for power and currentdistribution and improved temperature distribution (as described abovewith respect to FIGS. 16-19 and 20A-20C); and the temperature controlsubsystem for maintaining the electrolyte temperature during operationof the cell in response to changes in current density (as describedabove with respect to FIG. 21 )—allow the overall water electrolysis H₂gas generation system to be flexible and dynamically accommodate a widerange of operational parameters. Specifically, the structural andsystematic aspects described herein can allow the electrolyzer cells tooperate over a wide range of current densities while still being able toaccommodate a wide disparity in heat generation, temperaturefluctuation, and gas production rate. For example, electrolyzer cellscomprising one or more of these features can operate at a currentdensity over a dynamic range of from as low as about 150 milliamps persquare centimeter (mA/cm²) to as high as about 3000 mA/cm², such as fromabout 250 mA/cm² to about 2750 mA/cm², for example from about 500 mA/cm²to about 2500 mA/cm², such as from about 750 mA/cm² to about 2250mA/cm², for example from about 1000 mA/cm² to about 2000 mA/cm². Thestructural and systematic aspects described herein also allow theelectrolyzer cells to accommodate a wide range electrolyte flow ratesand gas production rates while still reducing or minimizing slug or plugflow of the electrolyte or the produced gas through the electrolyzercells and/or exiting the electrolyzer cells.

These structural and systematic aspects can allow the electrolyzer cellsto be operated at a current density that is higher than a specifiedcurrent density and/or at a H₂ gas production rate that is higher than aspecified gas production rate (i.e., the “nominal” current densityand/or the “nominal” H₂ gas production rate for the electrolyzer cell orfor the plant as a whole) during a period when demand for electricityand/or the price of electricity is below a specified threshold and/orwhen demand for electricity and/or the price of electricity isdecreasing, which will also be referred to hereinafter as “loadgaining,” to take advantage of situations where the demand forelectricity and/or the price of electricity is below a specifiedthreshold . Likewise, the electrolyzer cells are configured to beoperated at a current density that is lower than a specified currentdensity and/or at a H₂ gas production rate that is lower than aspecified gas production rate (i.e., the “nominal” current densityand/or the “nominal” H₂ gas production rate for the electrolyzer cell orfor the plant as a whole) during a period when demand for electricityand/or the price of electricity is above a specified threshold and/orwhen price and/or demand is increasing, which will also be referred tohereinafter as “load shedding,” to take advantage of situations wherethe demand for electricity and/or the price of electricity is above thespecified threshold or when price or demand is increasing. In someexamples, the electrolyzer described herein is configured to operatewithin a range of current density values of 0.15 A/cm² and 3.0 A/cm².However, it should be understood that other ranges and values of currentdensity are suitable for use with the electrolyzer and methods describedherein including current density values above 3.0 A/cm² and/or below0.15 A/cm².

As will be appreciated by those having skill in the art, the price ordemand of electricity can vary greatly depending on the location of theelectrolyzer cells. Therefore, unless stated otherwise herein, the terms“price” or “demand,” as used herein when referring to electricity, arethe price or demand of electricity within the relevant region in whichthe electrolyzer cells are located.

The electrolyzer cells described herein can also be manufactured atrelatively low capital expenditures (“CapEx”) compared to conventionalwater-splitting electrolysis cells. As used herein, the terms “capitalexpenditures” and “CapEx” refers to capital expenses incurred toengineer, design, procure, and construct the electrolyzer cells andsupporting equipment (e.g., piping, deionized water generation, pumpsfor electrolyte and water circulation, gas processing and storage,electricity rectifiers, electricity transformers, and electricitybussing).

The relatively low CapEx cost required to design and construct theelectrolyzer cells of the present disclosure can allow the electrolyzercells to be designed to be capable of accommodating a maximum currentdensity that is higher than the “nominal” current density, e.g., thecurrent density associated with an optimum current density for which theelectrolyzer cells are being designed (which corresponds to a nominaldesired H₂ gas production rate for which the overall plant is beingdesigned). In other words, if the total plant is designed for an averageH₂ gas production capacity (corresponding to a particular cell size andnominal current density), then the cells can be designed with one ormore of the structure features described above that allow theelectrolyzer cell to achieve a higher current density (and thus a higherH₂ gas production rate) without making the design of the cellsuneconomical. For example, the designed H₂ gas production rate for theentire plant may translate to a nominal operating current density ofabout 1 A/cm². But in accordance with the present disclosure, theelectrolyzer cells can be designed so that they can handle asubstantially larger current density, such as a current density of about1.5 A/cm² or higher, for example about 1.6 A/cm² or higher, such asabout 1.7 A/cm² or higher, for example about 1.75 A/cm² or higher, suchas about 1.8 A/cm² or higher, for example about 1.9 A/cm² or higher,such as about 2 A/cm² or higher, for example about 2.1 A/cm² or higher,such as about 2.2 A/cm² or higher, for example about 2.25 A/cm² orhigher, such as about 2.3 A/cm² or higher, for example about 2.4 A/cm²or higher, such as about 2.5 A/cm² or higher, for example about 2.6A/cm² or higher, such as about 2.7 A/cm² or higher, for example about2.75 A/cm² or higher, such as about 2.8 A/cm² or higher, for exampleabout 2.9 A/cm² or higher, such as about 3 A/cm² or higher, for exampleabout 3.1 A/cm² or higher, such as about 3.2 A/cm² or higher, forexample about 3.25 A/cm² or higher, such as about 3.3 A/cm² or higher,for example about 3.4 A/cm² or higher, such as about 3.5 A/cm² or higherin order to be able to take advantage of electricity demand and/orprices that are below a specified threshold and/or a decreasing demandand/or price in a load gaining situation. Similarly, the supportingequipment for the cells (e.g., piping, deionized water generation, pumpsfor electrolyte and water circulation, gas processing and storage,electricity rectifiers, electricity transformers, and electricitybussing) may be “oversized” relative to what would be required for thenominal H₂ gas production rate and nominal current density in order totake advantage of potential load gaining situations and the higher heatdistribution and larger H₂ gas handling requirements associated withload gaining.

The relatively low CapEx of the electrolyzer cells described herein andtheir supporting equipment are such that it can still be economical,from a capital investment perspective, to operate the electrolyzer cellsof the present disclosure at a current density that is lower than aspecified current density and/or at a H₂ gas production rate that islower than a specified gas production rate (which can be the same ordifferent from the specified current density or the specified H₂ gasproduction rate associated with a load gaining situation, for examplethe specified current density can be certain percentage of the nominalcurrent density and/or the specified H₂ gas production rate can be acertain percentage of the nominal H₂ gas production rate) when carryingout load shedding in order to reduce the overall operating expenditures(“OpEx”) when the demand and/or price of electricity is above athreshold and/or increasing demand and/or price. As used herein, theterms “operating expenditures” and “OpEx” refer to the ongoing cost ofgenerating hydrogen gas with the electrolyzer cells and other supportingequipment, which can include, but is not limited to, electricity costs,operations labor, regular ongoing maintenance, insurance, engineeringand supervision operations, short-term consumables, and sales andadministration expenses. In contrast, typical electrolyzer cells havinghigher CapEx costs cannot economically produce hydrogen in a loadshedding situation, even though it reduces the OpEx, because the CapExof the typical electrolyzer cells are so high.

The electrolyzer cells and overall system of the present disclosureallow for dynamic control over the current density at which theelectrolyzer cells are capable of effectively and efficiently loadshedding and load gaining compared to existing electrolyzer cells. Asdescribed in more detail below, the ability of the electrolyzer cells tooperate over a wide range of current densities and gas production ratesallows the systems and methods described herein to provide for strategicand dynamic operation of the electrolyzer cells for H₂ gas production sothat the average cost for H₂ gas production is reduced and in someinstances minimized over the course of long-range operation of thesystem. In an example, the electrolyzer cells can be designed to beoperated at a maximum current density (which results in a correspondingmaximum H₂ gas production rate) that is 1 amp per square centimeter(A/cm²) or more, for example a maximum achievable current density ofabout 1.5 A/cm², for example a maximum achievable current density ofabout 2.0 A/cm², for example about 2.5 A/cm², for example a maximumachievable current density of about 3 A/cm² for example a maximumachievable current density of about 3.5 A/cm². In addition, theelectrolyzer cells and overall system of the present disclosure canallow for economic operation at a minimum economically-viable currentdensity (which results in a corresponding minimum H₂ gas productionrate) of about 750 milliamps per square centimeter (mA/cm²) or less, forexample a minimum economically-viable current density of about 600mA/cm², for example a minimum economically-viable current density ofabout 500 mA/cm², for example a minimum economically-viable currentdensity of about 400 mA/cm², such as a minimum economically-viablecurrent density of about 300 mA/cm², for example a minimumeconomically-viable current density of about 250 mA/cm², for example aminimum economically-viable current density of about 200 mA/cm², forexample a minimum economically-viable current density of about 150mA/cm². Therefore, in an example where the maximum achievable currentdensity for the electrolyzer cells is about 3 A/cm² (or about 3000mA/cm²) and a minimum economically-viable current density of about 150mA/cm², then the electrolyzer cell is able to operate as low as about 5%of the maximum achievable current density (i.e., 150 mA/cm² being 5% of3000 mA/cm²), which means that the electrolyzer cells have a loadshedding and load gaining operating range of 95% (i.e., from 5% to 100%of the maximum achievable current density).

The electrolyzer cell's ability to dynamically operate at high currentdensity and low current density can allow the operator to dynamicallyrespond to electricity prices and/or electricity demand and load gainwhen electricity prices and/or demand are low and/or are decreasing andload shed when electricity prices and/or demand are high and/or areincreasing. For example, if the demand for electricity increases over aperiod of time, then the OpEx for the electrolyzer cell will increase bya corresponding amount over the same period of time due to an increasein the price of electricity unless the operating current density of theelectrolyzer cell is dynamically decreased. Thus, in a load sheddingsituation, the dynamic lowering of the current density has the effect ofdynamically reducing the OpEx to counteract the expected rise in OpExassociated with the increase in demand.

In other words, the operating current density of the electrolyzer cellscan be changed in response to a period of time when the demand forelectricity and/or the price of electricity is fluctuating. Fluctuationin demand can include increases in demand (e.g., wherein demand during afirst period of time is lower than during a subsequent second period oftime) or decreases in demand (e.g., wherein demand during a first periodof time is higher than during a subsequent second period of time).Similarly, fluctuation in price can include increases in price (e.g.,wherein the price of electricity during a first period of time is lowerthan during a subsequent second period of time) or decreases in price(e.g., wherein the price of electricity during a first period of time ishigher than during a subsequent second period of time). The dynamicoperation of the electrolyzer cells can be particular useful duringperiods of time where the demand for electricity and/or the price ofelectricity is known to fluctuate (i.e., is known to increase ordecrease), such as during a time period spanning from the night time tomid-to-late afternoon.

The electrolyzer cells can be designed to achieve a maximum capacity. Asused herein, the term “maximum capacity,” when referring to theelectrolyzer cells, refers to the maximum current density that theelectrolyzer cell can reliably achieve (taking into account the abilityof the electrolyzer cell to dissipate generated heat in order to avoidor minimize damage to the cell's separator and/or to remove gas beingproduced within the cell without slug or plug flow of the gas or theelectrolyte). In an example, the maximum capacity current density is 1.5A/cm² or more, for example 1.6 A/cm² or more, 1.7 A/cm² or more, 1.75A/cm² or more, 1.8 A/cm² or more, 1.9 A/cm² or more, 2 A/cm² or more,2.1 A/cm² or more, 2.2 A/cm² or more, 2.25 A/cm² or more, 2.3 A/cm² ormore, 2.4 A/cm² or more, 2.5 A/cm² or more, 2.6 A/cm² or more, 2.7 A/cm²or more, 2.75 A/cm² or more, 2.8 A/cm² or more, 2.9 A/cm² or more, 3A/cm² or more, 3.1 A/cm² or more, 3.2 A/cm² or more, 3.25 A/cm² or more,3.3 A/cm² or more, 3.4 A/cm² or more, or 2.5 A/cm².

In an example, “load shedding” (i.e., situations where the operatingcurrent density of the electrolyzer cells is reduced in response to highor increasing electricity demand or price) includes reducing theoperating current density of the electrolyzer cell to 30% or less of themaximum capacity, for example 29% or less of the maximum capacity, 28%or less of the maximum capacity, 27% or less of the maximum capacity,26% or less of the maximum capacity, 25% or less of the maximumcapacity, 24% or less of the maximum capacity, 23% or less of themaximum capacity, 22% or less of the maximum capacity, 21% or less ofthe maximum capacity, 20% or less of the maximum capacity, 19% or lessof the maximum capacity, 18% or less of the maximum capacity, 17.5% orless of the maximum capacity, 17% or less of the maximum capacity, 16%or less of the maximum capacity, 15% or less of the maximum capacity,14% or less of the maximum capacity, 13% or less of the maximumcapacity, 12.5% or less of the maximum capacity, 12% or less of themaximum capacity, 11% or less of the maximum capacity, 10% or less ofthe maximum capacity, 9% or less of the maximum capacity, 8% or less ofthe maximum capacity, 7.5% or less of the maximum capacity, 7% or lessof the maximum capacity, 6% or less of the maximum capacity, or 5% orless of the maximum capacity.

In an example, “load gaining” (i.e., situations where the operatingcurrent density of the electrolyzer cells is increased in response tolow or decreasing electricity demand or price) includes increasing theoperating current density to 70% or more of the maximum capacity, 75% ormore of the maximum capacity, 76% or more of the maximum capacity, 77%or more of the maximum capacity, 77.5% or more of the maximum capacity,78% or more of the maximum capacity, 79% or more of the maximumcapacity, 80% or more of the maximum capacity, 81% or more of themaximum capacity, 82% or more of the maximum capacity, 82.5% or more ofthe maximum capacity, 83% or more of the maximum capacity, 84% or moreof the maximum capacity, 85% or more of the maximum capacity, 86% ormore of the maximum capacity, 87% or more of the maximum capacity, 87.5%or more of the maximum capacity, 88% or more of the maximum capacity,89% or more of the maximum capacity, 90% or more of the maximumcapacity, 91% or more of the maximum capacity, 92% or more of themaximum capacity, 92.5% or more of the maximum capacity, 93% or more ofthe maximum capacity, 94% or more of the maximum capacity, 95% or moreof the maximum capacity, 96% or more of the maximum capacity, 97% ormore of the maximum capacity, 97.5% or more of the maximum capacity, 98%or more of the maximum capacity, 98.5% or more of the maximum capacity,99% or more of the maximum capacity, 99.5% or more of the maximumcapacity, 99.9% or more of the maximum capacity, or to the maximumcapacity (i.e., to 100% of the maximum capacity).

In an example, the electrolyzer system (i.e., comprising all of theelectrolyzer cells in the plant) can generate at least about 1 kilogramof H₂ gas per hour (kg H₂/hr), such as at least about 1.5 kg Hz/hr, atleast about 5 kg Hz/hr, at least about 10 kg Hz/hr, at least about 25 kgHz/hr, at least about 50 kg Hz/hr, at least about 100 kg H₂/hr, at leastabout 500 kg H₂/hr, at least about 1000 kg Hz/hr, at least about 1500 kgHz/hr, at least about 2000 kg Hz/hr, at least about 2500 kg Hz/hr, atleast about 3000 kg Hz/hr, at least about 3500 kg Hz/hr, at least about4000 kg Hz/hr, at least about 4500 kg Hz/hr, or at least about 5000 kgHz/hr. In an example, the electrolyzer system can generate up to about30000 kg Hz/hr, for example up to about 25000 kg Hz/hr, up to about20000 kg Hz/hr, up to 15000 kg Hz/hr, or up to 10000 kg Hz/hr. As willbe appreciated by a person of skill in the art, the actual mass of H₂gas produced by the electrolyzer system will depend on many factorsincluding the area of each electrolyzer cell, the number of electrolyzercells in the electrolyzer system, and the current density at which theelectrolyzer cells are being operated. In an example, the mass of H₂ gasthat can theoretically generated per ampere of current supplied to theelectrolyzer cells is about 3.761×10⁻⁵ kg Hz/hr. Therefore, thetheoretical mass of H₂ gas that the electrolyzer system can generate isequal to the total amps supplied for electrolysis, which in turn isequal to the current density being applied to the electrolyzer cellsmultiplied by the total area of the elecrtrolyzer cells (or the area perelectrolyzer cell times the number of cells times the current density).

As explained in more detail below, the ability to dynamically load gainand load shed can result in the overall average cost of H₂ gasproduction per kilogram ($/kg) to be lower than is possible withconventional electrolyzer cells operated in a steady-state manner. Insome examples, described in more detail below, the dynamic load gainingand load shedding of the present disclosure can allow for a reduction offrom about 20% to about 40% or more (e.g., even as much as 50% or more)in the cost of electricity required to produce the same amount of H₂gas.

FIG. 22 is a graph illustrating typical prices of electricity over atwenty-four hour period (e.g., from midnight to midnight of thefollowing day), according to data collected by the Electric ReliabilityCouncil of Texas (“ERCOT”). Data line 400 represents the average priceof electricity, in United States dollars per megawatt hour ($/MWh), at aparticular time in the day. Data lines 402 and 404 represents onestandard deviation above and one standard deviation below the averageprice at each particular time in the day, respectively. As can be seenby FIG. 22 , the price of electricity tends to remain relatively steadyfrom hour 1 (i.e., midnight) until about hour 10 (i.e., 9 AM), at whichpoint the average price goes up rather steeply to above $60/MWh and witha large variation. The high average price and high variability remainsuntil about hour 19 or hour 20 (e.g., 6-7 PM), at which point theaverage price begins to drop back down toward the more stable priceexperienced at the beginning of the day. In other words, the price ofelectricity tends to be low and has little variance during nighttime andearly morning hours and then tends to go up and have large variabilityduring mid-day and afternoon hours. The ability to dynamically operatethe electrolyzer cells by load shedding and load gaining can allow theoperator to, for example, operating the electrolyzer cells at high load(i.e., high current density, e.g., above a specified current density,such as above 1 A/cm²) during periods of low electricity pricing (i.e.,during the night time such as from hours 1-10 and after about hour 22 inthe graph of FIG. 22 ) and then operating the electrolyzer cells at lowload (i.e., low current density, e.g., below the specified currentdensity) during periods of high electricity pricing (i.e., during theday time from hours 10-22 in the graph of FIG. 22 ) can allow thesystems and methods described herein to dynamically respond toelectricity prices and, as described below, to achieve an overallelectricity cost that is less than what would be incurred byconventional, steady-state operation.

FIG. 23 shows an example scenario involving changes in electricitypricing and how the systems and methods described herein can bedynamically operated in load gaining and load shedding manners in orderto reduce the overall average price of H₂ gas production compared toconventional operation of electrolyzer cells at a constant orsubstantially constant current density and H₂ gas production rate thatdoes not take into account the current price of electricity. Data line406 corresponds to the fluctuating price of electricity over the courseof two full days of operation. Line 408 is a data series of theoperating current density of the electrolyzer cells according to thepresent disclosure at various times over the course of the same two dayswhen the electrolyzer cells are being operated to load gain duringperiods when the electricity price is below a specified lower pricethreshold (e.g., about $25 per MWh in the example of FIG. 23 ), wherethe current density is ramped down when the price of electricity goesabove the specified lower price threshold, and where the electrolyzercells are shut off (i.e., operated at a current density of 0 A/cm²) whenthe price of electricity goes above a specified upper price threshold(e.g., about $40 per MWh in the example of FIG. 23 ). Data line 410corresponds to the “nominal” current density at which the electrolyzercells are designed to be operated (e.g., “about 1 A/cm” for the exampleof FIG. 23 ). In other words, data line 410 represents “conventional”operation of the electrolyzer cells at the capacity for which they weredesigned. As can be seen in FIG. 23 , if the electrolyzer cells werecontinually operated at the nominal current density, then the averageprice of electricity over the two days represented by the data of FIG.23 would be $28 per MWh.

In the example of FIG. 23 , the electrolyzer cells are operated at aload gaining current density (e.g., about 2 A/cm²) when the electricityprice is below the specified lower price threshold (e.g., when the priceis ≤$25 per MWh in the example of FIG. 23 ), at a variable load sheddingcurrent density when the price of electricity is between the specifiedlower price threshold and the specified upper price threshold (e.g.,when the price is between $25/MWh and $40/MWh in the example of FIG. 23, the current density is set somewhere between 0 and 2 A/cm² dependingon the electricity price), and are shut down if the price is above thespecified upper price threshold (e.g., a current density of 0 A/cm² whenthe price is greater than $40/MWh in the example of FIG. 23 ). In theexample scenario shown in FIG. 23 , the average current density over thecourse of the two days was about 1.6 A/cm² (as represented by data line412), which is about 60% higher than the nominal current density of 1A/cm² during conventional operation of the electrolyzer cells (e.g.,above the current density associated with data line 410). Moreover, theaverage cost of the electricity consumed over the course of the two daysof operation was about $22 per MWh (represented by data line 414), whichcorresponds to about a 20% reduction in the cost of electricity duringthe load gaining and load shedding operation of the present disclosure.In other words, in the example scenario shown in FIG. 23 , not only wasthe electricity cost substantially lower than conventional operation ofthe electrolyzer cells (i.e., about $22/MWh versus about $28/MWh, or 20%less electricity cost over the same period of time), the sameelectrolyzer cells were able to achieve a substantially higher averagecurrent density (i.e., about 1.6 A/cm² on average versus 1 A/cm², orabout 60% higher). As will be appreciated by those having skill in theart, this means that the same electrolyzer cells were also able toproduce substantially more H₂ gas (because the production rate of H₂ gasis proportional to the current density) at a substantially loweroperating cost.

The example scenario and the threshold electricity prices of FIG. 23 areprovided for illustrative purposes only and are not intended to limitthe scope of the present disclosure. Those having skill in the art willappreciate that the operating current densities of the electrolyzercells and the threshold electricity prices that trigger adjustment ofthe operating current density can be varied and will still beencompassed by the present disclosure. As noted above, the electrolyzercells that can be incorporated into the load gaining and load sheddingsystems and methods of the present disclosure can operate over a widerange of current densities, for example from a lower limit of about 0.15A/cm² up to an upper limit of 3 A/cm² or more. This large dynamic rangeof operating current densities can allow an operator with considerableflexibility to choose a minimum electricity price threshold at which tostart the transition from a load gaining current density to a loadshedding current density and a maximum electricity price threshold atwhich to operate a load shedding current density or to shut of theelectrolyzer cells completely, and to include one or more additionalintermediate price thresholds at which to set one or more intermediateoperating current densities.

Those having skill in the art may also appreciate that the specificoperating current density for each price threshold can be selected basedon aspects of the specific electrolyzer cells, including, but notlimited to: an optimal current density for the particular electrolyzercell (e.g., the current density that is most efficient at producing H₂gas on the basis of the mass of H₂ gas produced per MW of electricityconsumed, which itself can depend on the price of electricity), amaximum current density that the electrolyzer cell can achieve (e.g.,depending on the electrolyzer cell's ability to remove the gas producedand/or dissipate the heat generated), or the cost per kilogram of H₂ gasproduced for the electrolyzer cells at various current densities and atvarious electricity prices per MWh.

FIGS. 24 and 25 show examples of these considerations for a particularelectrolyzer cell. FIG. 24 shows a cost curve (represented by line 416)for a particular example electrolyzer cell. The cost curve 416corresponds to the total levelized cost per kilogram of H₂ gas producedat different operating current densities when the price of electricityis $26.6/MWh. For this example, electrolyzer cell, the cost curve 416has a minimum point 418 at a current density of about 1.12 A/cm²,corresponding to a production cost of about $1.91 per kg of H₂ gasproduced. The cost curve 416 in FIG. 24 corresponds to the cost if theelectrolyzer cell was operated at a constant current density rather thanthe cost if the load gaining and load shedding methods of the presentdisclosure are being practiced. In other words, the cost curve 416corresponds to the example electrolyzer cell being operated in theconventional manner, similar to the line 410 of FIG. 23 . If, however,the load gaining and load shedding method of the present disclosure ispracticed (e.g., similar to the example described above with respect toFIG. 23 ), then the effective optimum current density for the sameexample electrolyzer cell (at data point 420) rises to about 1.66 A/cm²(an increase of about 40% over the 1.19 A/cm² for the minimum point 418on the conventional cost curve 416) and the average cost per kilogram ofH₂ is reduced to about $1.69/kg H₂ (a reduction of about 11.5% comparedto the $1.91/kg H₂ for the minimum point 418 on the conventional costcurve 416).

FIG. 25 shows a graph of the optimum current density (represented bydata line 422) for a particular example electrolyzer cell as a functionof the price of electricity. As used herein, the term “optimum currentdensity” refers to the current density that achieves the minimum costper kilogram of H₂ produced at a particular electricity price. In anexample, the optimum current density for each electricity price can bedetermined in much the same way as was performed in FIG. 24 , e.g., byfinding a minimum point on the cost curve associated with eachelectricity price. In the example of FIG. 25 , when the price is belowabout $35/MWh (or $0.035/kWh), the optimum current density is at orabove the maximum current density for which the example electrolyzercell can operate, so that when the price is below $35/MWh, theelectrolyzer cell can be run at its maximum current density of about 2 A/cm² (e.g., the electrolyzer cell can be operated in a full load gainingmanner). At a price of about $35/MWh, the optimum current density beginsto go down as the price rises such that, in an example, the operatingcurrent density for the electrolyzer cell can be ramped down as theelectricity price rises above $35/MWh. In other words, in the example ofFIG. 25 , $35/MWh is the specified lower price threshold correspondingto the start of the transition between load gaining and load shedding(as described above with respect to FIG. 23 ). As shown in FIG. 25 ,when the price of electricity reaches about $50/MWh, the optimum currentdensity for the example electrolyzer cell reaches zero (0) (ignoringother considerations such as the costs of shutdown and startup labor,wear on the plant equipment, and the like). Therefore, when the price ishigher than $50/MWh, the example electrolyzer cell can be shut down. Inother words, in the example of FIG. 25 , $50/MWh is the specified upperprice threshold (as described above with respect to FIG. 23 ). Thosehaving skill in the art will appreciate that the exact price point forthe specified upper price threshold can be varied from the actual pricepoint where the optimum current density reaches zero, and the amount ofvariance can depend on one or more factors including, but not limitedto, the capital expenditure for the example electrolyzer cells and othersupporting equipment (e.g., the CapEx), the overall size of theelectrolyzer cells in the plant (e.g., the size of the cell stack), thecurrent price at which the produced H₂ gas can be sold, and otheroperating expenses (such as the cost of labor to run the plant or toshut down and startup the plant or the price of water, or the cost ofregular maintenance for the electrolyzer cells and the supportingequipment). In fact, the “optimum” current density at any point alongthe optimum current density curve 422 can be varied from the theoreticalor calculated optimum current density based on one or more of these samefactors.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An electrolyzer system comprising: one or moreelectrolyzer cells each comprising a first half cell with a firstelectrode and a second half cell with a second electrode; and acontroller to control a current applied through the one or moreelectrolyzer cells; wherein the controller is configured to dynamicallyset the current density within a current density range of from about 150mA/cm² to about 3000 mA/cm², and wherein the controller is configured toset the current density to a first value when a first condition is metand to a second value when a second condition is met.
 2. An electrolyzersystem according to claim 1, wherein the first value is at or below afirst percentage of a maximum capacity current density of theelectrolyzer cell and the second value is at or above a secondpercentage of the maximum capacity current density of the electrolyzercell.
 3. An electrolyzer system according to claim 2, wherein the firstpercentage is 20% or less of the maximum capacity current density.
 4. Anelectrolyzer system according to claim 2, wherein the second percentageis 80% or more of the maximum capacity current density.
 5. Anelectrolyzer system according to claim 1, wherein the first half cellcomprises a pan, one or more ribs inside the pan, and a baffle platecoupled to the one or more ribs, wherein the baffle plate partitions avolume in the pan to provide a riser region on a first side of the panproximate to the first electrode and a down-comer region on a secondside of the baffle plate opposite the first side.
 6. An electrolyzersystem according to claim 5, wherein the riser region facilitates gasformed at the first electrode to rise and avoid formation of gaspockets, and wherein the down-comer region facilitates downward flow ofan electrolyte solution, wherein the rise of the gas and the downwardflow of the electrolyte solution causes circulation in the pan thatfacilitates thermal equilibrium and reduced temperature variation in theelectrolyte.
 7. An electrolyzer system according to claim 1, wherein thefirst half cell comprises a pan, a manifold positioned inside the pan,and an outlet tube exiting the manifold for electrolyte to exit the pan,wherein a cross-sectional area of the manifold is configured so that anelectrolyte flow rate and a gas flow rate through the manifold are lowenough to avoid slug flow or plug flow.
 8. An electrolyzer systemaccording to claim 1, wherein the first half cell comprises a pan, oneor more ribs positioned vertically inside the pan, and a plurality ofwelds that weld the first electrode to the one or more ribs, wherein theplurality of welds form a distributed array of welds across theelectrode that distribute current across the electrode during operationof the electrochemical cell.
 9. An electrolyzer system according toclaim 9, wherein each electrolyzer cell further comprises a separatorbetween the first half cell and the second half cell, wherein a number,size, and positions of the plurality of welds are such that an impact ofpower dissipation on a temperature of the separator is reduced to reducedamage due to high local temperature.
 10. An electrolyzer systemcomprising: a plurality of electrolyzer cells, wherein each electrolyzercell comprises; a first half cell with a first electrode; a second halfcell with a second electrode; and a separator separating the first halfcell from the second half cell; a power supply configured to apply acurrent through each of the plurality of electrolyzer cells so that acurrent density through each of plurality of electrolyzer cells iswithin a current density range of from about 150 mA/cm² to about 3000mA/cm²; a controller to dynamically control the current density of eachof the plurality of electrolyzer cells between a first current densityrange of 750 mA/cm² or less and a second current density range of 1mA/cm² or more.
 11. An electrolyzer system according to claim 10,wherein the first half cell comprises a pan, one or more ribs inside thepan, and a baffle plate coupled to the one or more ribs, wherein thebaffle plate partitions a volume in the pan to provide a riser region ona first side of the pan proximate to the first electrode and adown-comer region on a second side of the baffle plate opposite thefirst side.
 12. An electrolyzer system according to claim 10, whereinthe first half cell comprises a pan, a manifold positioned inside thepan, and an outlet tube exiting the manifold for electrolyte to exit thepan, wherein a cross-sectional area of the manifold is configured sothat an electrolyte flow rate and a gas flow rate through the manifoldare low enough to avoid slug flow or plug flow.
 13. An electrolyzersystem according to claim 10, wherein the first half cell comprises apan, one or more ribs positioned vertically inside the pan, and aplurality of welds that weld the first electrode to the one or moreribs, wherein the plurality of welds form a distributed array of weldsacross the electrode that distribute current across the electrode duringoperation of the electrochemical cell.
 14. An electrolyzer systemaccording to claim 13, wherein each electrolyzer cell further comprisesa separator between the first half cell and the second half cell,wherein a number, size, and positions of the plurality of welds are suchthat an impact of power dissipation on a temperature of the separator isreduced to reduce damage due to high local temperature.
 15. A method forcarrying out electrolysis comprising: dynamically changing a currentdensity associated with an operation of an electrolyzer within a rangeof values of about 0.15 A/cm² and 3.0 A/cm²; wherein the changing of thecurrent density associated with the operation of the electrolyzer is inresponse to a change in demand for electricity within a region where theelectrolyzer is located; and wherein the changing of the current densitycomprises lowering the current density within the range of values ofabout 0.15 A/cm² and 3.0 A/cm² when the demand for electricity increaseswithin the region where the electrolyzer is located and raising thecurrent density within the range of values of about 0.15 A/cm² and 3.0A/cm² when the demand for electricity decreases within the region wherethe electrolyzer is located.
 16. The method of claim 15, wherein thechange in demand occurs for a period of time when the demand isfluctuating.
 17. The method claim 16, wherein the demand fluctuatingcomprises increases and decreases of demand within the period of time.18. The method of claim 17, wherein an average demand over the period oftime is elevated compared to another period of time.
 19. The method ofclaim 17, wherein an average demand over the period of time is decreasedcompared to another period of time.
 20. The method of claim 17, whereinthe period of time is one where demand typically increases or decreases.21. The method of claim 20, wherein the period of time is betweenspecific hours within a day.
 22. The method of claim 15, wherein theelectrolyzer comprises at least two separate electrolyzer cells.
 23. Themethod of claim 15, wherein the electrolyzer has a total size of atleast about 2.5 m³.
 24. The method of claim 15, wherein when the demandfor electricity increases within the region where the electrolyzer islocated, an operating expenditure of the electrolyzer increases unlessthe current density is decreased.